AU2012326283A1

AU2012326283A1 - Restricted immunoglobulin heavy chain mice

Info

Publication number: AU2012326283A1
Application number: AU2012326283A
Authority: AU
Inventors: Cagan Gurer; Lynn Macdonald; John Mcwhirter; Karolina A. Meagher; Andrew J. Murphy
Original assignee: Regeneron Pharmaceuticals Inc
Current assignee: Regeneron Pharmaceuticals Inc
Priority date: 2011-10-17
Filing date: 2012-10-17
Publication date: 2013-05-16
Anticipated expiration: 2032-10-17
Also published as: AU2012326283C1; CN104024418B; KR20190090886A; AU2016204127C1; DK3216871T3; EP3216871A1; IL292030A; RS62942B1; IL292030B2; US20200277371A1; JP2020202873A; MX355062B; RU2016139418A; CN108207807A; JP2019068836A; AU2018203811A1; EP2627773A1; AU2016204127B2; IL265967A; IL292030B1

Abstract

Mice having a restricted immunoglobulin heavy chain locus are provided, wherein the locus is characterized by a single polymorphic human V

Description

LUUIWL INU. U.3IUPVV/ RESTRICTED IMMUNOGLOBULIN HEAVY CHAIN MICE FIELD [0001] Non-human animals that are genetically engineered at an immunoglobulin heavy chain variable (V) region locus (or in a transgene) to make antibodies from a restricted number of immunoglobulin heavy chain variable (VH) segments (or a single VH segment) and/or variants thereof. Non-human animals that have a human heavy chain variable domain derived from a single immunoglobulin heavy chain variable gene segment, e.g., human immunoglobulin VH1 69 gene segment or human VH1-2 gene segment. Methods for making antibody sequences in non-human animals that are useful for binding pathogens, including human pathogens. BACKGROUND [0002] Non-human animals, e.g., mice, have been genetically engineered to be useful tools in methods for making antibody sequences for use in antibody-based human therapeutics. Mice with humanized variable region loci (e.g., VH, DH, and JH genes, and VL and JL genes) are used to generate cognate heavy and light chain variable domains for use in antibody therapeutics. Other mice are available that generate fully human antibodies with cognate heavy and light chains. [0003] Human antibody therapeutics are engineered based on desired characteristics with respect to certain pre-selected antigens. Humanized mice are immunized with the pre-selected antigens, and the immunized mice are used to generate antibody populations from which to identify high-affinity cognate heavy and light variable domains with desired binding characteristics. Some humanized mice, such as those having a humanization of just variable regions at endogenous mouse loci, generate populations of B cells that are similar in character and number to wild-type mouse B cell populations. As a result, an extremely large and diverse population of B cells is available in these mice from which to screen antibodies, reflecting a large number of different immunoglobulin rearrangements, to identify heavy and light variable domains with the most desirable characteristics. [0004] But not all antigens provoke an immune response that exhibits a very large number of rearrangements from a wide selection of variable (V) segments. That is, the human humoral immune response to certain antigens is apparently restricted. The restriction is reflected in clonal selection of B cells that express only certain V segments that bind that particular antigen with sufficiently high affinity and specificity. Some such antigens are clinically significant, i.e., a number are well-known human pathogens. A presumption arises that the V segment expressed in the human immune response is a V segment that, in combination with a human D and a human J segment, is more likely to generate a useful high affinity antibody than a 1 LUV1A1WL 1VU. 10 IA1/fW\ randomly selected V segment that has not been observed in a human antibody response to that antigen. [0005] It is hypothesized that natural selection, over millennia, has selected the most efficient foundation or base from which to design a most effective weapon for neutralizing human pathogens-a clonally selected V segment. There is a need in the art for more and superior antibodies that bind and/or neutralize antigens such as the pathogens discussed above. There is a need to more rapidly generate useful sequences from selected V segments, including polymorphic and/or somatically mutated selected V segments and to more rapidly generate useful populations of B cells having rearrangements of the V segments with various D and J segments, including somatically mutated versions thereof, and in particular rearrangements with unique and useful CDR3s. There is a need for biological systems, e.g., non-human animals (such as, e.g., mice, rats, rabbits, etc.) that can generate therapeutically useful antibody variable region sequences from pre-selected V segments in increased number and diversity than, e.g., can be achieved in existing modified animals. There is a need for biological systems engineered to have a committed humoral immune system for clonally selecting antibody variable sequences derived from restricted, pre-selected V segments, including but not limited to cognate human heavy and light chain variable domains, useful in the manufacture of human antibody-based therapeutics against selected antigens, including certain human pathogens. [0006] There is a need in the art for therapeutic antibodies that are capable of neutralizing viral antigens, e.g., HIV and HCV, including antigen-specific antibodies containing heavy chains derived from a single human variable segment, and for a system that produces a diverse source of antibodies from which to select therapeutic antibody sequences. There is also a need for further methods and non-human animals for making useful antibodies, including antibodies that comprise a repertoire of heavy chains derived from a single human VH segment and having a diverse set of CDR sequences, and including such heavy chains that express with cognate human light chain variable domains. Methods are needed for selecting CDRs for immunoglobulin-based binding proteins that provide an enhanced diversity of binding proteins from which to choose, and enhanced diversity of immunoglobulin variable domains, including compositions and methods for generating somatically mutated and clonally selected immunoglobulin variable domains for use, e.g., in making human therapeutics. SUMMARY [0007] Genetically modified immunoglobulin loci are provided that comprise a restricted number of different heavy chain variable region gene segments (i.e., V genes, VH genes, VH gene segments, or V gene segments), e.g., no more than one, two, or three different V genes; 2 LJUUKUL 1MU. IJ.)I UMVVWI or no more than one V gene segment family member present, e.g., in a single copy or in multiple copies and/or comprising one or more polymorphisms. [0008] Loci are provided that are capable of rearranging and forming a gene encoding a heavy chain variable domain that is derived from a VH gene repertoire that is restricted, e.g., that is a single VH gene segment or selected from a plurality of polymorphic variants of the single VH gene segment. Modified immunoglobulin loci include loci that comprise human immunoglobulin sequences are provided, e.g., a human V segment operably linked to a human or (or human/non-human chimeric) non-human immunoglobulin constant sequence (and in operable linkage with, e.g., a D and/or a J segment). Modified loci that comprise multiple copies of a single VH gene segment, including wherein one or more of the copies comprises a polymorphic variant, are provided. Modified loci that comprise multiple copies of a single VH segment, operably linked with one or more D segments and one or more J segments, operably linked to a non-human immunoglobulin constant sequence, e.g., a mouse or rat sequence, are provided. Non-human animals comprising such humanized loci are also provided. [0009] Non-human animals are provided that have a reduced immunoglobulin heavy chain variable gene segment complexity (i.e., a limited number of heavy chain variable gene segments, or a limited heavy chain variable gene repertoire), wherein the reduced immunoglobulin heavy chain variable gene segment complexity is characterized by the presence of no more than one or no more than two heavy chain variable gene segments, and wherein the heavy chain variable genes present are operably linked to a human or non-human constant region sequence. [00010] Non-human animals are provided that have a reduced immunoglobulin heavy chain variable gene segment complexity (e.g., a single VH gene segment, or a limited number of VH gene segments that are polymorphic variants of a single VH gene segment), wherein the reduced immunoglobulin heavy chain variable gene segment complexity is characterized by the presence of a single VH gene segment or a plurality of VH gene segments that are polymorphic forms of a single VH gene segment (e.g., VH gene segments associated with high copy number and/or polymorphism in humans), and wherein the heavy chain variable genes present are operably linked to a human or non-human constant region sequence. In various embodiments, the heavy chain variable genes present are operably linked to one or more D and/or one or more J gene segments in the germline of the non-human animal. [00011] Non-human animals are provided that comprise an immunoglobulin heavy chain variable locus (e.g., on a transgene or as an insertion or replacement at an endogenous non human animal heavy chain variable locus) that comprises a single VH segment operably linked to a D and/or J gene segment. In various embodiments, the single VH gene segment is operably linked to one or more D and/or one or more J gene segments at the endogenous immunoglobulin heavy chain variable gene locus of the non-human animal. 3 WL/UUIWL 1MU. 1,0fU/A-V/ [00012] Non-human animals are provided that are modified at their immunoglobulin heavy chain variable region loci to delete all or substantially all (e.g., all functional segments, or nearly all functional segments) endogenous immunoglobulin VH segments and that comprise a human VH1-69 segment (or a human VH1-2 segment) operably linked to a D and J segment or a J segment at the endogenous immunoglobulin heavy chain variable region locus of the non human animal. [00013] Non-human animals are also provided that are modified at their immunoglobulin heavy chain variable region loci to render the endogenous variable region loci incapable of rearranging to form a functional heavy chain comprising endogenous variable region gene segments; wherein the non-human animals comprise a single human variable gene segment (a human VH1-2 or a human VH1-69 gene segment) operably linked to a D and a J segment or a J segment at the endogenous immunoglobulin heavy chain variable region locus of the non human animal. [00014] Non-human animals are provided that comprise a restricted number (e.g., no more than one, or no more than two) of heavy chain gene segments operably linked to a human or non-human constant region sequence. In one embodiment, the no more than one or no more than two heavy chain gene segments linked to the constant region sequence are on a transgene, e.g., are at a position other than an endogenous heavy chain locus. [00015] Methods are provided for making human immunoglobulin sequences in non-human animals. In various embodiments, the human immunoglobulin sequences are derived from a repertoire of immunoglobulin V sequences that consist essentially of a single human V segment, e.g., VH1-69 or VH1-2, and one or more D and J segments or one or more J segments. Methods for making human immunoglobulin sequences in non-human animals, tissues, and cells are provided, wherein the human immunoglobulin sequences bind a pathogen. [00016] Methods are provided for making mice characterized by a restricted immunoglobulin heavy chain locus, wherein the restriction is with respect to the number of immunoglobulin VH gene segments. In various aspects, the restriction is to one or no more than two, or a single VH gene family member (e.g., one or more VH alleles, variants, or polymorphic variants thereof). In various aspects, the heavy chain locus further comprises one or more DH gene segments and one or more JH gene segments. In various aspects, the VH, DH and JH gene segments are human. In various aspects, the VH, DH and JH gene segments are operably linked to a non human constant region (e.g., an IgM and/or an IgG). In various aspects, the constant region is a mouse or rat constant region. [00017] In one aspect, a method for making a mouse having a restricted immunoglobulin heavy chain locus is provided, comprising introducing a nucleic acid construct as described 4 IJUUKUL 14U. I3#IUP.-VV herein into a mouse embryonic stem (ES) cell, and isolating or identifying a mouse ES cell that comprises the nucleic acid construct. [00018] In one embodiment, the nucleic acid construct comprises a single human VH gene segment, one or more human DH gene segments, and one or more human JH gene segments. In one embodiment, the nucleic acid construct comprises one or more site-specific recombination sites (e.g., a loxP or a Frt site). [00019] In one aspect, a mouse made using a targeting vector, nucleic acid sequence, or cell as described herein is provided. In various embodiments, the targeting vector, nucleic acid sequence or cell comprises a DNA sequence that contains a single human VH gene segment (or polymorphic variants thereof), one or more human DH gene segments, and one or more human JH gene segments operably linked to a non-human constant gene. [00020] In one aspect, a method for making a mouse comprising a restricted immunoglobulin heavy chain locus is provided, comprising replacing a mouse immunoglobulin heavy chain locus with a human genomic sequence comprising a single human VH gene segment (or polymorphic variants thereof), one or more human DH gene segments, and one or more human JH gene segments, wherein the human VH, DH and JH gene segments are capable of rearranging to form a chimeric heavy chain that contains a human variable domain operably linked to a non-human constant region. In one embodiment, the non-human constant region is a mouse or rat constant region. [00021] In various aspects, the non-human animals are rodents. In various aspects, the rodents are mice and/or rats. [00022] In one aspect, a modified immunoglobulin heavy chain locus is provided that comprises a heavy chain V segment repertoire that is restricted with respect to the identity of the V segment, and that comprises one or more D segments and one or more J segments, or one or more J segments. In one embodiment, the heavy chain V segment is a human segment. In one embodiment, the one or more D segments are human D segments. In one embodiment, the one or more J segments are human J segments. In one embodiment, the one or more D segments and one or more J segments are human D and human J segments. [00023] In one embodiment, the modified locus is a non-human locus. In one embodiment, the non-human locus is modified with at least one human immunoglobulin sequence. [00024] In one embodiment, the restriction is to one V segment family member. In one embodiment, the one V segment family member is present in two or more copies. In one embodiment, the one V segment family member is present as two or more variants (e.g., two or more polymorphic forms of the V segment family member). In one embodiment, the one V segment is a human V segment family member. In one embodiment, the one V segment family member is present in a number of variants as is observed in the human population with respect to that variant. In one embodiment, the V segment family member is selected from Table 1. In 5 L/OUKUI INO. 1' U4-VVIJ one embodiment, the V segment family member is present in a number of variants as shown, for each V segment, in a number of alleles from 1 allele to the number of alleles shown in the right column of Table 1. [00025] In one embodiment, the restriction is to a human VH1-69 gene segment. In one embodiment, the human VH1-69 gene segment is present in two or more copies. In one embodiment, the human VH1 -69 gene segment is present as two or more variants (e.g., two or more polymorphic forms the human VH1-69 gene). In one embodiment, the human VH1- 6 9 gene segment is present in a number of variants as is observed in the human population with respect to the human VH1-69 gene segment. In one embodiment, the human VH1-69 gene segment is selected from Table 2. In one embodiment, the human VH1-69 gene segment is present in a number of variants as shown, for each VH1-69 gene segment, in a number of alleles from one allele to the number of alleles shown in Table 2. [00026] In one embodiment, the restriction is to a human VH1-2 gene segment. In one embodiment, the human VH1-2 gene segment is present in two or more copies. In one embodiment, the human VHi-2 gene segment is present as two or more variants (e.g., two or more polymorphic forms the human VH1-2 gene). In one embodiment, the human VH1- 2 gene segment is present in a number of variants as is observed in the human population with respect to the human VH1- 2 gene segment. In one embodiment, the human VH1-2 gene segment is selected from Table 3. In one embodiment, the human VH1-2 gene segment is present in a number of variants as shown, for each VH1-2 gene segment, in a number of alleles from one allele to the number of alleles shown in Table 3. [00027] In one aspect, a heavy chain immunoglobulin locus is provided that comprises a single functional human V segment. In one embodiment, the single functional human V segment is selected from a VH1- 2 , VH1-3, VH1-8, VH1-18, VH1-24, VH1-45, VH1-46, VH1-58, VH1 69, VH2-5, VH 2

-

2 6 , VH2-70, VH3-7, VH3-9, VH3-11, VH3-13, VH3-15, VH3-16, VH3-20, VH3-21, VH3-23, VH3-30, VH 3

-

3 0- 3 , VH3-30-5, VH3-33, VH3-35, VH3-38, VH3-43, VH3-48, VH3-49, VH3-53, VH3-64, VH3-66, VH 3

-

7 2 , VH3-73, VH3-74, VH4-4, VH4-28, VH4-30-1, VH4-30-2, VH4-30-4, VH4 31, VH4-34, VH4-39, VH4-59, VH4-61, VH5-51, VH6-1, VH7-4-1, and a VH7-81 segment. In one embodiment, the single functional human V segment is a VH1 -69 segment; in a specific embodiment, the single functional human V segment is present in 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, or 13 polymorphic forms found in the human population. In one embodiment, the single functional human V segment is a VH1- 2 segment; in a specific embodiment, the single functional human V segment is present in 1, 2, 3, 4, or 5 polymorphic forms found in the human population. [00028] In one embodiment, the heavy chain immunoglobulin locus is a modified locus of a non-human animal. In one embodiment, the modified non-human immunoglobulin heavy chain locus is present in the non-human animal at a position in the genome in which the 6 LJU%;t|PRL INU. I a I UM-VV %J corresponding unmodified non-human locus is found in the wild-type non-human animal. In one embodiment, the modified non-human immunoglobulin heavy chain locus is present on a transgene in a non-human animal. [00029] In one embodiment, the single functional human V gene segment is a VH1-69 gene segment. In one embodiment, the VH1-69 gene segment comprises SEQ ID NO: 34. In one embodiment, the VH1-69 gene segment is derived from SEQ ID NO: 34. In one embodiment, the VHI- 6 9 gene segment is at least 80%, at least 85%, at least 90%, at least 95%, or at least 98% identical to SEQ ID NO: 34. [00030] In one embodiment, the single functional human V gene segment is encoded by the nucleotide sequence of SEQ ID NO: 34. [00031] In one embodiment, the single functional human V gene segment is a VH1-2 gene segment. In one embodiment, the VH1-2 gene segment comprises SEQ ID NO: 60. In one embodiment, the VH1-2 gene segment is derived from SEQ ID NO: 60. In one embodiment, the VH1- 2 gene segment is at least 80%, at least 85%, at least 90%, at least 95%, or at least 98% identical to SEQ ID NO: 60. [00032] In one embodiment, the single functional human V gene segment is encoded by the nucleotide sequence of SEQ ID NO: 60. [00033] In one embodiment, the single functional human V segment is operably linked to one or more D segments and one or more J segments, or one or more J segments. In one embodiment, the V segment and one or more D and/or J segments are operably linked to an immunoglobulin heavy chain constant region sequence. In one embodiment the immunoglobulin heavy chain constant region sequence is selected from a CH1, a hinge, a CH 2 , a CH 3 sequence, and a combination thereof. In one embodiment, the CH1, hinge, CH 2 , 0

H

3 , or combination thereof are each non-human endogenous constant sequences. In one embodiment, at least one of the CH 1 , hinge, CH 2 , CH 3 , or combination thereof is a human sequence. In a specific embodiment, the CH 1 and/or hinge are human sequences. [00034] In one aspect, a modified endogenous non-human immunoglobulin heavy chain locus is provided, comprising a replacement of all functional V gene segments with a single human V gene segment (or a single human V gene segment present in multiple polymorphic forms or copy number), wherein the non-human immunoglobulin heavy chain locus is incapable of rearrangement to form a heavy chain variable gene that is derived from a V gene segment other than the single human V gene segment (or one of the polymorphic forms or copies). [00035] In one embodiment, the single human V gene segment is VHi-69. In one embodiment, the single human V gene segment is VH1-2. [00036] In one embodiment, the locus comprises at least one human or non-human DH gene segment, and one human or non-human JH gene segment. In a specific embodiment, the locus comprises a human DH gene segment and a human JH gene segment. In a specific 7 IJOCK01 INO. '1,5IVIA-VVV4 embodiment, the locus comprises a human JH gene segment. In another specific embodiment, the locus comprises a human VH1 -69 gene segment (present as a single copy or multiple copies of different polymorphic variants), all functional human DH gene segments, and all functional human JH gene segments. In another specific embodiment, the locus comprises a human VH1-2 gene segment (present as a single copy or multiple copies of different polymorphic forms), all functional human DH gene segments, and all functional human JH gene segments. In one embodiment, the human V, D, and J gene segments (or V and J gene segments) are operably linked to a mouse constant region gene at an endogenous mouse heavy chain locus. In a specific embodiment, the mouse heavy chain locus comprises a wild type repertoire of mouse immunoglobulin constant region sequences. [00037] In one aspect, a genetically modified non-human animal is provided, wherein the only functional immunoglobulin heavy chain V gene segment of the non-human animal is selected from a human VH1-2, VH1-3, VH1- 8 , VH1-18, VH1-24, VH1-45, VH1-46, VH1-5 8 , VH1-69, VH2-5, VH2-26, VH2-70, VH3-7, VH3-9, VH3-1 1, VH3-13, VH3-15, VH3-16, VH3- 2 0 , VH3-21, VH3-23, VH3-30, VH3-30-3, VH3-30-5, VH3-33, VH3-35, VH3-38, VH3-43, VH3-48, VH3-49, VH3-53, VH3- 64 , VH3-66, VH3-72, VH3-73, VH3-74, VH4-4, VH4-28, VH4-30-1, VH4-30-2, VH4-30-4, VH4-31, VH4 34, VH4-39, VH4-59, VH4-61, VH5-51, VH6-1, VH7-4-1, and VH7-81 gene segment. In one embodiment, the heavy chain V gene segment is a human VHi-69 gene segment. In one embodiment, the heavy chain V gene segment is a human VH1-2 gene segment. [00038] In one aspect, a genetically modified non-human animal is provided, wherein the non-human animal comprises a single functional human VH gene segment (present as a single copy or multiple copies of different polymorphic forms), and wherein the non-human animal is substantially incapable of forming a rearranged immunoglobulin heavy chain variable domain gene that lacks the single functional human VH gene segment (or one of the polymorphic forms or copies). [00039] In one aspect, a genetically modified non-human animal is provided, wherein the only immunoglobulin heavy chain variable region expressed in the non-human animal is derived from one of a human segment selected from a human VH1-2, VH1-3, VH1-8, VH1-18, VH1-24, VH1-45, VH1-46, VH1-58, VH1-69, VH 2 -5, VH2-26, VH2-70, VH3-7, VH3-9, VH3-11, VH3-13, VH3-15, VH3-16, VH3-20, VH3-21, VH3-23, VH3-30, VH3-30-3, VH3-30-5, VH3-33, VH3-35, VH3-38, VH3-43, VH3-48, VH3-49, VH3-53, VH3-64, VH3-66, VH3-72, VH3-73, VH3-74, VH4-4, VH4-28, VH4 30-1, VH4-30-2, VH4-30-4, VH4-31, VH4-34, VH4-39, VH4-59, VH4-61, VH5-51, VH6-1, VH7-4-1, and VH7-81 gene segment. In one embodiment, the human segment is a VH1-69 segment. In one embodiment, the human segment is a VH1-2 segment. In one embodiment, the only immunoglobulin heavy chain variable region expressed by the mouse is derived from a single V segment family member, and in one embodiment the only immunoglobulin heavy chain variable region is derived from a polymorphic variant of the single V segment family member. 8 IJOCKUT IN0. '1.)/ UA-VVU [00040] In one aspect, a non-human animal comprising a restricted immunoglobulin heavy chain V gene segment repertoire is provided, wherein the non-human animal further comprises one or more human immunoglobulin K light chain variable segments (VK). In one embodiment, the one or more Vx segments are operably linked to one or more human J segments. In a specific embodiment, the J segments are human JK segments. In another specific embodiment, the non-human animal does not express an immunoglobulin X light chain. In another specific embodiment, the non-human animal does not comprise a functional human or functional endogenous immunoglobulin X light chain variable locus. [00041] In one embodiment, the non-human animal is a rodent. In one embodiment, the rodent is a mouse. [00042] In one embodiment, the non-human animal comprises a replacement at the endogenous non-human immunoglobulin VK locus of all or substantially all functional endogenous Vx segments with one or more functional human VK segments. In a further specific embodiment, the replacement is with all or substantially all functional human immunoglobulin Vx segments. [00043] In one embodiment, the non-human animal comprises a replacement at the endogenous non-human immunoglobulin Vic locus of all or substantially all functional endogenous Vx gene segments with human Vi gene segments selected from VK4-1, VK5-2, VK7-3, VK 2

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4 , VK1- 5 , VO1-6, Vw3-7, VO1-8, VO1-9, VK 2 -10, VO3-11, VK1-12, Vx1-13, Vx2-14, V3-15, Vx1-16, Vw1 -17, VK 2 -1 8 , Vx2-19, V3-20, VK6-21, VK1 -22, V1 -23, VK2-24, VK 3

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2 5 , VK2-26, V1- 2 7 , VW 2

-

2 8 , VK 2

-

2 9 , V2-30, VK 3

-

3 1, VK1-32, VK1-33, Vw3-34, VK1-35, VK2-36,

VKI-

3 7 , VK 2

-

3 8 , VK1-39, VK 2

-

4 0, and a combination thereof. [000441 In one embodiment, the non-human animal comprises a replacement at the endogenous non-human immunoglobulin JK locus of all or substantially all functional endogenous non-human immunoglobulin JK segments with one or more functional human immunoglobulin JK segments. In a further specific embodiment, the replacement is with all or substantially all functional human immunoglobulin JK segments. [00045] In one embodiment, the non-human animal comprises a replacement at the endogenous non-human immunoglobulin JK locus of all or substantially all functional endogenous non-human immunoglobulin JK gene segments with human JK gene segments selected from JK1, JK2, JK3, JK4, JK5, and a combination thereof. [00046] In a specific embodiment, the non-human animal comprises an immunoglobulin heavy chain variable region locus that comprises a repertoire of V segments consisting essentially of a single V segment and/or polymorphic variants thereof. In one embodiment, the single immunoglobulin heavy chain V segment is a human VH1-69 segment, and the non 9 LJOUUL 14. 1.3 D I -VVV/ human animal further comprises a replacement of all functional non-human DH segments with all functional human DH segments, and further comprises a replacement of all functional non human JH segments with all functional human JH segments, and wherein the immunoglobulin heavy chain variable region locus is operably linked to a human or non-human constant region gene sequence. In a specific embodiment, the constant region gene sequence is an endogenous non-human constant region gene sequence. In a specific embodiment, the non human animal rearranges segments at the non-human immunoglobulin heavy chain locus to form a gene encoding heavy chain variable region comprising a human VH1-69 sequence, a human DH sequence, a human JH sequence, and a mouse constant region sequence. [00047] In a specific embodiment, the non-human animal comprises an immunoglobulin heavy chain variable region locus that comprises a repertoire of V segments consisting essentially of a single V segment and/or polymorphic variants thereof. In one embodiment, the single immunoglobulin heavy chain V segment is a human VH1-2 segment, and the non-human animal further comprises a replacement of all functional non-human DH segments with all functional human DH segments, and further comprises a replacement of all functional non human JH segments with all functional human JH segments, and wherein the immunoglobulin heavy chain variable region locus is operably linked to a human or non-human constant region gene sequence. In a specific embodiment, the constant region gene sequence is an endogenous non-human constant region gene sequence. In a specific embodiment, the non human animal rearranges segments at the non-human immunoglobulin heavy chain locus to form a gene encoding heavy chain variable region comprising a human VH1- 2 sequence, a human DH sequence, a human JH sequence, and a mouse constant region sequence. [00048] In one embodiment, a B cell is provided that comprises the rearranged gene. In a specific embodiment, the B cell is from a mouse as described that has been immunized with an antigen of interest, and the B cell encodes an antibody that specifically binds the antigen of interest. In one embodiment, the antigen of interest is a pathogen. In a specific embodiment, the pathogen is selected from an influenza virus, a hepatitis virus (e.g., hepatitis B or hepatitis C virus), and a human immunodeficiency virus. In a specific embodiment, the B cell encodes a somatically mutated, high affinity (e.g., about 10) KD or lower) antibody comprising a human light chain variable region (e.g., a human x light chain variable region) that specifically binds the antigen of interest. [00049] In one aspect, a non-human animal comprising a restricted immunoglobulin heavy chain V segment repertoire is provided, wherein the non-human animal comprises one or more human X light chain variable (VW) segments. In one embodiment, the one or more human V segments are operably linked to one or more human J segments. In a specific embodiment, the J segments are human JX segments. In another specific embodiment, the non-human 10 IOCKUI 140. 'IO5IU/4-VVI animal does not express a K light chain. In another specific embodiment, the non-human animal does not comprise a functional human or non-human i light chain variable locus. [00050] In one embodiment, the non-human animal comprises a replacement of all or substantially all functional non-human immunoglobulin VX segments with one or more functional human immunoglobulin Vk segments. In a further specific embodiment, the replacement is with all or substantially all functional human immunoglobulin VX segments. [00051] In one embodiment, the non-human animal comprises a replacement of all or substantially all functional non-human VA segments with a fragment of cluster A of the human 4 light chain locus. In a specific embodiment, the fragment of cluster A of the human k light chain locus comprises human VX gene segments Vk3-27 through V3-1. [00052] In one embodiment, the non-human animal comprises a replacement of all or substantially all functional non-human VX segments with a fragment of cluster B of the human k light chain locus. In a specific embodiment, the fragment of cluster B of the human K light chain locus comprises human VX gene segments V5-52 through Vk1-40. [00053] In one embodiment, the non-human animal comprises a replacement of all or substantially all functional non-human VX segments with a fragment of cluster A and a fragment of cluster B of the human k light chain locus, wherein as a result of the replacement comprise human VX gene segments Vk5-52 through V3-1. [00054] In one embodiment, the non-human animal comprises a replacement of all or substantially all functional non-human Vk segments with at least 12 human Vk gene segments, at least 28 human Vk gene segments, or at least 40 human Vk gene segments. [00055] In one embodiment, the non-human animal comprises a replacement of all or substantially all functional non-human immunoglobulin Jk gene segments with one or more functional human immunoglobulin Jk gene segments. In a further specific embodiment, the replacement is with all or substantially all functional human immunoglobulin JK gene segments. In various embodiments, the functional human J gene segments include J1, Jk2, Jk3 and JX7. [00056] In a specific embodiment, the non-human animal comprises an immunoglobulin heavy chain variable (VH) region locus that comprises only a single VH segment, wherein the single VH segment is a human VH1-69 segment or a human VH1-2 segment, and further comprises a replacement of all functional non-human DH segments with all functional human DH segments, and further comprises a replacement of all functional non-human JH segments with all functional human JH segments, and wherein the VH region locus is operably linked to a human or non-human constant region gene sequence. In a specific embodiment, the constant region gene sequence is a non-human constant region gene sequence, e.g., an endogenous 11 LJUUr L I1U. I )I U -VV W non-human constant gene sequence. In a specific embodiment, the non-human animal rearranges segments at the non-human immunoglobulin heavy chain locus to form a gene encoding an immunoglobulin heavy chain variable region comprising a human VH1-69 sequence (or a human VH1- 2 sequence), a human DH sequence, a human JH sequence, and an endogenous non-human constant region sequence. [00057] In one embodiment, a B cell is provided that comprises the rearranged gene. In a specific embodiment, the B cell is from a non-human animal as described that has been immunized with an antigen of interest, and the B cell encodes an antibody that specifically binds the antigen of interest. In one embodiment, the antigen is a human protein selected from a ligand, a cell surface receptor and an intracellular protein. In one embodiment, the antigen of interest is a pathogen. In a specific embodiment, the pathogen is selected from an influenza virus, a hepatitis virus (e.g., hepatitis B or hepatitis C virus), and a human immunodeficiency virus. In a specific embodiment, the B cell encodes a somatically mutated, high affinity (e.g., about 10-9 KD or lower) antibody comprising a human light chain variable region (e.g., a human X light chain variable region) that specifically binds the antigen of interest. [00058] In one aspect, a non-human animal comprising a restricted immunoglobulin VH segment repertoire is provided, wherein the non-human animal comprises a human VH1-69 segment (or a human VH1-2 segment) on a transgene, wherein the human VH1- 6 9 segment is operably linked on the transgene to a human or non-human DH segment, and/or a human or non-human J segment, and the transgene further comprises a human or non-human constant region gene, or a chimeric human/non-human constant region (e.g., a CHi, hinge, CH 2 , CH 3 or combination thereof wherein at least one sequence is non-human, e.g., selected from hinge, CH2, and OH 3 and/or hinge). In one embodiment, the non-human animal is a mouse or rat and the non-human D, J, and/or constant region gene is a mouse or rat gene or chimeric human/mouse or rat. [00059] In one embodiment, the non-human animal comprises a transgene that comprises an immunoglobulin light chain variable region locus that comprises one or more human immunoglobulin VX gene segments and JX gene segments, or one or more human immunoglobulin Vx gene segments and JK gene segments, and a human immunoglobulin K or X light chain constant region gene, such that the transgene rearranges in the non-human animal to form a rearranged immunoglobulin K or X light chain gene. In various embodiments, the human Vx and JK gene segments are those described herein. In various embodiments, the human V and JR gene segments are those described herein. [00060] In a specific embodiment, the non-human animal comprises a transgene having an immunoglobulin heavy chain variable locus that comprises a single V segment that is a human VH1-69 segment (or a human VH1-2 segment), one or more human D segments, one or more 12 LJO CKeT, WO. 'I J iU/4-VVU% human J segments, and a human constant gene operably linked to the heavy chain variable locus, such that the mouse expresses from the transgene a fully human antibody derived from the VH1- 6 9 segment (or the VH1-2 segment). In one embodiment, the non-human animal does not comprise a functional endogenous immunoglobulin heavy chain variable region locus. In a specific embodiment, the non-human animal comprises a nonfunctional endogenous immunoglobulin heavy chain variable region locus that comprises a deletion of an endogenous non-human DH and/or endogenous non-human JH segment, such that the non-human animal is incapable of rearranging the endogenous immunoglobulin heavy chain variable region locus to form a rearranged non-human antibody gene. In a specific embodiment, the non-human animal comprises a deletion of a switch sequence operably linked to an endogenous mouse heavy chain constant region. In a specific embodiment, the switch sequence is a non-human (e.g., mouse) t switch sequence. In another embodiment, the non-human animal further comprises a lack of a functional endogenous light chain variable locus selected from an immunoglobulin K locus and an immunoglobulin k locus. In a specific embodiment, the non human animal comprises a deletion of a JK and/or a JX sequence, such that the non-human animal is incapable of rearranging an endogenous non-human immunoglobulin K light chain and/or an endogenous non-human immunoglobulin k light chain variable region to form a rearranged endogenous non-human immunoglobulin K light chain and/or a rearranged endogenous non-human immunoglobulin k light chain gene. [00061] In one embodiment, the non-human animal comprises a deletion of an endogenous non-human immunoglobulin K light chain sequence that results in a functional knockout of the endogenous non-human immunoglobulin K light chain. In one embodiment, the non-human animal comprises a deletion of an endogenous non-human immunoglobulin k light chain sequence that results in a functional knockout of the endogenous non-human immunoglobulin k light chain. [00062] In one aspect, the non-human animal comprises a functionally silenced endogenous immunoglobulin heavy chain variable gene locus, and comprises a restricted repertoire of human heavy chain variable gene segments (e.g., no more than one, or no more than two). In one embodiment, the functional silencing comprises a modification of an endogenous non human heavy chain variable gene locus selected from a deletion, an insertion, an inversion, and a combination thereof. [00063] In one aspect, a rodent is provided that comprises an immunoglobulin VH repertoire derived from no more than one human VH segment or one or more polymorphs thereof, from a D segment selected from a repertoire of one or more D segments, and from a J segment derived from a repertoire of one or more J segments. In one embodiment, the rodent rearranges the human VH segment, a human D segment, and a human J segment and forms a 13 UoCKeX NO. NI.,UA-VVU rearranged human heavy chain sequence that is operably linked to a human or a rodent constant region sequence. In one embodiment, the human and/or rodent constant region sequence is selected from a CH 1 , a hinge, a CH 2 , a CH 3 , and a combination thereof. In one embodiment, the rodent expresses an immunoglobulin light chain that comprises a human variable domain, wherein the light chain is cognate with a human heavy chain domain derived from the rearranged human heavy chain sequence. In one embodiment, the rodent does not express a polypeptide sequence selected from a non-human heavy chain variable domain, a non-human light chain variable domain, and a combination thereof. [00064] In one embodiment, the human VH segment is present in 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, or 19 or more polymorphic variants, wherein each polymorphic variant is operably linked to a D and/or J segment such that each polymorphic variant is capable for rearranging and forming a rearranged heavy chain variable domain with any of the one or more D segments and any of the one or more J segments. In one embodiment, the rodent is a mouse or a rat, In one embodiment, the repertoire of D segments comprises two or more D segments. In one embodiment, the repertoire of J segments comprises two or more J segments. In one embodiment, the D and/or J segments are human segments. [00065] In one aspect, a nucleic acid construct is provided that comprises a sequence encoding a single human immunoglobulin VH segment and/or polymorphic variants thereof and one or more DH and one or more J sequences, wherein the construct comprises at least one homology arm homologous to a non-human immunoglobulin heavy chain variable locus, or a recombinase recognition site (e.g., a lox site). In one embodiment, the V segment is a VH1-69 segment or a VH1-2 segment. [00066] In one aspect, a nucleic acid construct is provided; comprising a nucleic acid sequence encoding a single human immunoglobulin heavy chain V segment, wherein the single VH segment is a VH1-69 (or VH1-2) segment. In one embodiment, the construct comprises a site-specific recombinase recognition site. In one embodiment, the construct comprises a first mouse homology arm upstream of the VH1- 6 9 (or VH1-2) segment and a second mouse homology arm downstream of the VH1-69 (or VH1-2) segment, and wherein the first mouse homology arm is homologous to a region of a mouse chromosome immediately upstream of a mouse immunoglobulin heavy chain variable region but not including a functional mouse immunoglobulin heavy chain variable segment. In one embodiment, the construct comprises SEQ ID NO: 3. In one embodiment, the construct comprises SEQ ID NO: 70. [00067] In one aspect, the restricted single VH segment is in a non-human animal, or the restricted VH segment is at a non-human immunoglobulin heavy chain locus (e.g., in situ or in a transgene), and the non-human animal or non-human immunoglobulin heavy chain locus is selected from a mouse, rat, rabbit, pig, bovine (e.g., cow, bull, buffalo), deer, sheep, goat, 14 IUUCKU1 IN. 10 i U1AVVUA chicken, cat, dog, ferret, primate (e.g., marmoset, rhesus monkey) locus or animal. In a specific embodiment, the non-human animal or locus is a mouse or a rat locus. [00068] In one aspect, a cell or tissue is provided, wherein the cell or tissue is derived from a non-human animal as described herein, and comprises a restricted VH segment repertoire. In one embodiment, the VH segment repertoire is restricted to a single VH segment family member and/or polymorphic variants thereof. In a specific embodiment, the single VH segment is a human VHi-69 segment or a human VHi-2 segment. In one embodiment, the cell or tissue is derived from spleen, lymph node or bone marrow of the non-human animal. [00069] In one embodiment, the cell is an ES cell. In one embodiment, the cell is a B cell. In one embodiment, the cell is a germ cell. [00070] In one embodiment, the tissue is selected from connective, muscle, nervous and epithelial tissue. In a specific embodiment, the tissue is reproductive tissue. [00071] In one embodiment, the cell and/or tissue derived from a mouse as described herein are isolated for use in one or more ex vivo assays. In various embodiments, the one or more ex vivo assays include measurements of physical, thermal, electrical, mechanical or optical properties, a surgical procedure, measurements of interactions of different tissue types, the development of imaging techniques, or a combination thereof. [00072] In one embodiment, the non-human animal is a mouse. [00073] In one aspect, a non-human embryo is provided comprising a restricted heavy chain VH segments as described herein. In one embodiment, the embryo comprises an ES donor cell that comprises the restricted VH segment, and host embryo cells. [00074] In one embodiment, the non-human animal is a mouse. [00075] In one aspect, a non-human cell comprising a chromosome or fragment thereof of a non-human animal as described herein. In one embodiment, the non-human cell comprises a nucleus of a non-human animal as described herein. In one embodiment, the non-human cell comprises the chromosome or fragment thereof as the result of a nuclear transfer. [00076] In one aspect, a nucleus derived from a non-human animal as described herein is provided. In one embodiment, the nucleus is from a diploid cell that is not a B cell. [00077] In one aspect, a pluripotent, induced pluripotent, or totipotent cell derived from a non-human animal as described herein is provided. In a specific embodiment, the cell is a mouse embryonic stem (ES) cell. [00078] In one aspect, a non-human induced pluripotent cell comprising a restricted VH segment repertoire is provided. In one embodiment, the induced pluripotent cell is derived from a non-human animal as described herein. [00079] In one aspect, a hybridoma or quadroma is provided, derived from a cell of a non human animal as described herein. In one embodiment, the non-human animal is a mouse or rat. 15 IJOUKT INO. '1I UAR-VVU [00080] In one aspect, a lymphocyte of a non-human animal as described herein is provided. In one embodiment, the lymphocyte is a B cell. [00081] In one aspect, mouse cells and mouse embryos are provided, including but not limited to ES cells, pluripotent cells, and induced pluripotent cells, that comprise genetic modifications as described herein. Cells that are XX and cells that are XY are provided. Cells that comprise a nucleus containing a modification as described herein are also provided, e.g., a modification introduced into a cell by pronuclear injection. [00082] In one aspect, an antibody variable domain sequence made in a non-human animal as described herein is provided. [00083] In one aspect, a human therapeutic is provided, comprising an antibody variable domain comprising a sequence derived from a non-human animal as described herein. [00084] In one aspect, a method of obtaining an antibody variable region sequence from a non-human animal is provided, wherein the antibody variable region sequence is derived from a human VH1-69 segment or a VH1-2 segment, wherein the method comprises (a) immunizing a non-human animal with an antigen of interest, wherein the non-human animal comprises a replacement at the endogenous immunoglobulin heavy chain locus of all or substantially all non-human variable segments with a single human variable segment, wherein the single human variable segment is a VH1-69 segment or a VHi-2 segment, and wherein the non-human animal is substantially incapable of forming a immunoglobulin heavy chain variable region sequence that is not derived from a human VH1-69 segment or a VH1-2 segment; (b) allowing the non-human animal to mount an immune response with respect to the antigen of interest; and, (c) identifying or isolating an immunoglobulin heavy chain variable region sequence of the non-human animal, wherein the antibody binds the antigen of interest. [00085] In one embodiment, the single human variable segment is a VHl-69 segment. [00086] In one embodiment, the antibody variable region sequence is derived from SEQ ID NO: 34. In one embodiment, the antibody variable region sequence is at least 75%, at least 80%, at least 85%, at least 90%, at least 95%, or at least 98% identical to SEQ ID NO: 34. In one embodiment, the antibody variable region sequence comprises SEQ ID NO: 34. [00087] In one embodiment, the single human variable segment is a VH1-2 segment. [00088] In one embodiment, the antibody variable region sequence is derived from SEQ ID NO: 60. In one embodiment, the antibody variable region sequence is at least 75%, at least 80%, at least 85%, at least 90%, at least 95%, or at least 98% identical to SEQ ID NO: 60. In one embodiment, the antibody variable region sequence comprises SEQ ID NO: 60. [00089] In one embodiment, the immune response to the antigen is characterized by an antibody titer that is about 6x1 04 to about 5x1 05 times greater than two times background as determined in an ELISA assay. In a specific embodiment, the antibody titer is about 1x10 5 to about 2x10 5 times greater than two times background as determined in an ELISA assay. In a 16 L/UUIPWL 1nU. IQ/IUM-VV/ specific embodiment, the antibody titer is about 1.5x1 05 times greater than two times background as determined in an ELISA assay. In one embodiment, the antigen is a human cell surface receptor. [00090] In one aspect, a method for generating a repertoire of human antibody variable regions in a non-human animal is provided, wherein the human heavy chain variable regions of the repertoire are derived from the same VH gene family member and one of a plurality of DH segments and one of a plurality of JH segments, wherein the repertoire is characterized by having heavy chain immunoglobulin FRI (framework 1), CDR1, FR2, CDR2, and FR3 sequences from a single VH gene family member. In one embodiment, the repertoire is further characterized by having a plurality of different CDR3 + FR4 sequences. [00091] In one embodiment, the single VH gene family is selected from VH family 1, 2, 3, 4, 5, 6, and 7. In a specific embodiment, the single VH gene family is VH family 1. In one embodiment, the single VH gene family member is selected from VH1-2, VH1-69, VH2-26, VH2 70, and VH3-23. In a specific embodiment, the single VH gene family member is VH1- 6 9 . In a specific embodiment, the single VH gene family member is VH1-2. [00092] In one embodiment, the repertoire comprises heavy chain FRI, CDRI, FR2, CDR2 and FR3 sequences derived from a VHi-69 segment. In a specific embodiment, the repertoire comprises heavy chain FRI, CDR1, FR2, CDR2 and FR3 sequences derived from SEQ ID NO: 35. In a specific embodiment, the repertoire comprises heavy chain FRI, CDR1, FR2, CDR2 and FR3 sequences of SEQ ID NO: 35. [00093] In one embodiment, the repertoire comprises heavy chain FRI, CDR1, FR2, CDR2 and FR3 sequences derived from a VH1-2 segment. In a specific embodiment, the repertoire comprises heavy chain FRi, CDR1, FR2, CDR2 and FR3 sequences derived from SEQ ID NO: 61. In a specific embodiment, the repertoire comprises heavy chain FRI, CDR1, FR2, CDR2 and FR3 sequences of SEQ ID NO: 61. [00094] In one aspect, a biological (i.e., in vivo) system is provided for generating a plurality of different human CDR3 sequences reflecting a plurality of rearrangements of a single human VH gene segment with a plurality of human D and J segments, wherein the system generates human heavy chain variable domains characterized by having human FR1-CDR1-FR2-CDR2 FR3 sequences that are identical but for somatic hypermutations, wherein the heavy chain variable domains are characterized by being somatically hypermutated and derived from a single human VH gene segment and a plurality of human D and J segments; wherein the system comprises a genetically modified non-human animal (e.g., a rodent, e.g., a mouse or rat) as described herein. [00095] In one embodiment, the single human VH gene segment is selected from VH1-2, VH1-69, VH 2

-

2 6 , VH 2

-

7 0, and VH3-23. In one embodiment, the single human VH gene segment is VH1-69. In one embodiment, the single human VH gene segment is VH1-2. In one 17 LJOKfIe INO. 'I J I U/A-VVU embodiment, the single human VH gene segment is identified in Table 1. In one embodiment, the single human VH gene segment is identified in Table 2. In one embodiment, the single human VH gene segment is identified in Table 3. [00096] In one aspect, an in vivo method for generating a plurality of heavy chain CDR sequences derived from rearrangements of a single human VH gene segment with a plurality of human D and J segments is provided, wherein the method generates human heavy chain variable domains characterized by having human FR1-CDR1-FR2-CDR2-FR3 sequences that are identical but for somatic hypermutations, wherein the heavy chain variable domains are characterized by being somatically hypermutated and derived from a single human VH gene segment and a plurality of human D and J segments; wherein the system comprises a genetically modified non-human animal (e.g., a rodent, e.g., a mouse or rat) as described herein. [00097] In one embodiment, the method comprises exposing a non-human animal as described herein to an antigen of interest, allowing the non-human animal to develop an immune response to the antigen, wherein the immune response generates the plurality of heavy chain CDR sequences derived from rearrangements of the single human VH gene segment with one of the human D and one of the human J segments, and identifying a set of heavy chain CDRs that bind the antigen. In one embodiment, the method comprises isolating from the animal a nucleic acid sequence that encodes a human VH domain that comprises the heavy chain CDRs. [00098] In one embodiment, the heavy chain CDR sequences are derived from a rearrangement of a human VH1-69 gene segment. In one embodiment, the heavy chain CDR sequences are derived from a rearrangement of a human VH1-2 gene segment. [00099] In one aspect, a method for generating a plurality of different CDR3 and FR4 sequences in a non-human animal is provided, comprising exposing a non-human animal that comprises an immunoglobulin heavy chain variable gene locus with a VH segment repertoire restricted to a single VH segment family member to an antigen of interest, allowing the non human animal to develop an immune response to the antigen, wherein the immune response generates a B cell repertoire whose heavy chain variable domains are each derived from the single VH segment family member and that comprise a plurality of different CDR3 and FR4 sequences. [000100] In one embodiment, the singe VH segment family member is human. In one embodiment, the non-human animal is selected from a mouse, a rat, and a rabbit. In one embodiment, the antigen of interest is selected from a ligand, a receptor, an intracellular protein and a secreted protein. In one embodiment, the antigen of interest is a human pathogen as described herein. 18 LJOCKel IN0. 'Iof U/4-VVU [000101] In one embodiment, the single human VH gene family member is selected from VH1 2, VH1-6 9 , VH2-26, VH 2

-

7 0 , and VH3-23. In one embodiment, the single human VH gene family member is VH1-69. In one embodiment, the single human VH gene family member is VH1-2. In one embodiment, the single human VH gene family member is identified in Table 1. In one embodiment, the single human VH gene family member is identified in Table 2. In one embodiment, the single human VH gene family member is identified in Table 3. [000102] In one aspect, a nucleotide sequence encoding an immunoglobulin variable region made in a non-human animal as described herein is provided. [000103] In one aspect, an immunoglobulin heavy chain or immunoglobulin light chain variable region amino acid sequence of an antibody made in a non-human animal as described herein is provided. [000104] In one aspect, an immunoglobulin heavy chain or immunoglobulin light chain variable region nucleotide sequence encoding a variable region of an antibody made in a non human as described herein is provided. [000105] In one aspect, an antibody or antigen-binding fragment thereof (e.g., Fab, F(ab) 2 , scFv) made in a non-human animal as described herein is provided. [000106] In one aspect, a mouse having a restricted immunoglobulin heavy chain locus characterized by the presence of a single human VH gene segment, one or more human DH gene segments, and one or more human JH gene segments is provided, wherein the single human VH gene segment is at an endogenous mouse locus and the VH gene segment is operably linked to the one or more human DH gene segments, the one or more human JH gene segments, and to an endogenous immunoglobulin heavy chain constant gene. [000107] In one embodiment, the mouse further comprises a humanized immunoglobulin light chain locus comprising one or more human VL gene segments, and one or more human JL gene segments, wherein the human VL gene segments and the human JL gene segments are operably linked to a non-human immunoglobulin light chain constant region gene. In a specific embodiment, the human VL and JL gene segments are at an endogenous mouse light chain locus, and wherein the non-human immunoglobulin light chain constant region gene is a mouse gene. [000108] In one embodiment, the humanized immunoglobulin light chain locus is on a transgene, and the constant region gene is selected from mouse, rat, and human. [000109] In one embodiment, the human VL and JL gene segments are Vx and Jx gene segments. In one embodiment, the human VL and JL gene segments are V and JX gene segments [000110] In one aspect, a non-human animal is provided, wherein the non-human animal has a B cell repertoire that expresses immunoglobulin heavy chain variable domains derived from a 19 LJOUUe WO. 1 .31 V/--VVt/ single V segment family member. In one embodiment, at least 10%, at least 20%, at least 30%, at least 40%, at least 50%, at least 60%, at least 70%, at least 80%, at least 90, or at least 95% of the B cell repertoire of the non-human animal immunoglobulin heavy chain variable domain expressed in the B cell repertoire is derived from the same V segment family member. In a specific embodiment, the percentage is at least 90%. In one embodiment, the B cell repertoire consists essentially of peripheral (blood) B cells. In one embodiment, the B cell repertoire consists essentially of splenic B cells. In one embodiment, the B cell repertoire consists essentially of bone marrow B cells. In one embodiment, the B cell repertoire consists essentially of peripheral B cells, splenic B cells, and bone marrow B cells. [000111] In one aspect, a genetically modified non-human animal is provided, wherein more than 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or more than 90% of the B cells of the non human animal that express a heavy chain immunoglobulin variable domain express a heavy chain immunoglobulin variable domain derived from a single VH gene segment family member. In one embodiment, at least 75% of the B cells of the non-human animal that express an immunoglobulin heavy chain variable domain express an immunoglobulin heavy chain variable domain derived from the single VH gene segment family member. In a specific embodiment, the percentage is at least 90%. In one embodiment, all of the B cells that express a heavy chain domain that is derived from the single VH gene family member. [000112] In one aspect, a genetically modified mouse is provided that makes an antigen specific B cell population in response to immunization with an antigen of interest, wherein at least 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or more than 90%, of said antigen-specific B cell population expresses immunoglobulin heavy chains that are all derived from the same VH gene segment. In one embodiment, at least 75% of the antigen-specific B cell population expresses immunoglobulin heavy chains derived from the same VH gene segment. In one embodiment, all of the antigen-specific B cells express a heavy chain that is derived from the same VH gene segment. [000113] In one aspect, a non-human animal comprising a restricted VH gene segment repertoire is provided, wherein the restriction is to a human VH1-69 gene segment or a VH1-69 gene segment that is at least about 75.5%, 76.5%, 86.7%, 87.8%, 94.9%, 96.9%, 98%, or 99% identical to a VHi-69*01 gene segment. In a specific embodiment, the restricted repertoire is selected from one or more of the VH1-69 variants of FIG. 15. [000114] In one aspect, a non-human animal comprising a restricted VH gene segment repertoire is provided, wherein the restriction is to a human VH1-2 gene segment or a VH1-2 gene segment that is at least about 94.9%, 95.9%, 96.9%, 98%, or 99% identical to a VH1-2 gene segment. In a specific embodiment, the restricted repertoire is selected from one or more of the VHi- 2 variants of FIG. 18. [000115] In one embodiment, the non-human animal is a mouse. 20 LJOCKOe NO. 15fUA-VVV [000116] In one embodiment, the mouse exhibits an immunophenotype having a characteristic of a higher ratio of mature B cells to immature B cells as compared to a wild type mouse. In a specific embodiment, the ratio is calculated from B cells harvested from spleen. In one embodiment, the mouse exhibits a population of mature B cells of about 1x1 07. In one embodiment, the mouse exhibits a population of immature B cells of about 0.5x1 07. In one embodiment, the mouse exhibits a ratio of mature B cells to immature B cells in the spleen of the mouse that is about 1.5-fold to about 2-fold higher than exhibited by a wild type mouse. [000117] In one embodiment, the ratio is calculated from B cells harvested from bone marrow. In a specific embodiment, the mouse exhibits a population of mature B cells of about 3x1 0 In one embodiment, the mouse exhibits a population of immature B cells of about 7x10 5 . In one embodiment, the mouse exhibits a ratio of mature B cells to immature B cells in the bone marrow of the mouse that is about 3-fold, or about 3.3-fold higher than exhibited by a wild type mouse. [000118] In one embodiment, the mouse exhibits an immunophenotype having a characteristic of a higher number of pro B cells in the bone marrow as compared to a wild type mouse. In a specific embodiment, the mouse exhibits a population of pro B cells in the bone marrow of the mouse that is about 2.5-fold to about 3-fold higher than exhibited in the bone marrow of a wild type mouse. In a specific embodiment, the mouse exhibits a population of pro B cells in the bone marrow of the mouse that is about 2.75-fold higher than exhibited in the bone marrow of a wild type mouse. [000119] In one embodiment, the mouse exhibits an immunophenotype having a characteristic selected from the group consisting of a CD1 9' splenic B cell population that is about 80% of a wild-type B cell, a CD3 4 splenic T cell population that is about the same as a wild type mouse, and a combination thereof. [000120] In one embodiment, the mouse comprises a lymphocyte population whose % CD19* B cells in spleen are about the same as a wild-type mouse. In one embodiment, the number of CD1 9* B cells per spleen of the mouse is at least about 50% of the number of CD1 9* B cells per spleen of a wild-type mouse. [000121] In one embodiment, the non-human animal comprises at least about 75% to about 80% of CD19* B cells in bone marrow as compared with a wild-type mouse. [000122] In one embodiment, the total number of CD19* bone cells per femur of the mouse is non less than about 30%, 40%, 50%, 60%, or 75% of the total number of CD19+ bone marrow cells in a wild-type mouse. [000123] In one embodiment, the mouse expresses IgD and IgM at about the same level as observed in a wild-type mouse. [000124] In one aspect, a mouse comprising a restricted human VH segment repertoire is provided, further comprising a humanized immunoglobulin light chain variable segment locus, 21 LJOCKie INO. 'IJIUI-VVVU wherein the ratio of X to K light chains expressed in the mouse is about the same as in a wild type mouse. [000125] In one aspect, a mouse is provided, comprising a restricted immunoglobulin heavy chain locus characterized by the presence of a single VH gene segment, one or more DH gene segments, and one or more JH gene segments, wherein the single VH gene segment is a polymorphic VH gene segment. [000126] In one embodiment, the polymorphic VH gene segment is a human VH gene segment that is associated with a high copy number in human populations. In one embodiment, the human VH gene segment is selected from VH1-2, VH1-69, VH2-26, VH2-70, VH3-23, or a polymorphic variant thereof. In a specific embodiment, the human VH gene segment is a VH1-69 gene segment. In another specific embodiment, the human VH gene segment is a VH1-2 gene segment. [000127] In one embodiment, the single VH gene segment is operably linked to a human, mouse, or chimeric human/mouse immunoglobulin constant region gene. In a specific embodiment, the immunoglobulin constant region gene is a mouse constant region gene. In one embodiment, the immunoglobulin constant gene comprises a human sequence selected from a human CH1, a human hinge, a human CH 2 , a human CH 3 , and a combination thereof. In one embodiment, the mouse constant gene is at an endogenous immunoglobulin heavy chain locus. [000128] In one embodiment, the mouse further comprises a human immunoglobulin VL gene segment operably linked to a J gene segment and a light chain constant gene. In a specific embodiment, the VL gene segment and/or the J gene segment are selected from a human K gene segment and a human X gene segment. In one embodiment, the VL and/or J gene segments are human K gene segments. [000129] In various embodiments, the mouse comprises a deletion of all or substantially all endogenous VH gene segments. [000130] In various embodiments, the non-human animal comprises an inactivated endogenous heavy chain variable gene locus. In various embodiments, the inactivated endogenous heavy chain variable gene locus is not operably linked to an endogenous heavy chain constant region gene. [000131] In one aspect, a mouse is provided, wherein the mouse is characterized by the expression of serum immunoglobulin, wherein greater than 80% of the serum immunoglobulin comprises a human heavy chain variable domain and a cognate human light chain variable domain, wherein the human heavy chain variable domain is derived from a VH gene segment repertoire consisting essentially of a single human VH gene segment and/or polymorphic variants thereof. 22 UOCKoeT 4O. i1U/4-VVU [000132] In one embodiment, the single human VH gene segment is a human VH1-69 gene segment and/or polymorphic variants thereof. In one embodiment, the single human VH gene segment is a human VH1-2 gene segment and/or polymorphic variants thereof. [000133] In one aspect, a mouse is provided, comprising, in its germline, a replacement at an endogenous immunoglobulin heavy chain locus of all or substantially all endogenous VH gene segments with a single human VH gene segment and/or polymorphic variants thereof. In one embodiment, the single human VH gene segment is a human VH1 -69 gene segment and/or polymorphic variants thereof. In one embodiment, the single human VH gene segment is a human VH1- 2 gene segment and/or polymorphic variants thereof. [000134] In one embodiment, the mouse further comprises a replacement at an endogenous immunoglobulin light chain locus of all or substantially all endogenous VL gene segments with one or more human VL gene segments. In a specific embodiment, the mouse further comprises one or more human JL gene segments operably linked to the human VL gene segments. [000135] In one aspect, use of a mouse as described herein to make an immunoglobulin variable region nucleotide sequence is provided. In one embodiment, the sequence comprises a rearranged VH1-69 gene segment. In one embodiment, the sequence comprises a rearranged VH1-2 gene segment. [000136] In one embodiment, the immunoglobulin variable region nucleotide sequence is at least 80%, at least 85%, at least 90%, at least 95%, or at least 98% identical with a human VH1 69 gene segment. In a specific embodiment, the immunoglobulin variable region nucleotide sequence is at least 80%, at least 85%, at least 90%, at least 95%, or at least 98% identical with SEQ ID NO: 34. In various embodiments, the human VH1-69 gene segment is identified from Table 2. [000137] In one embodiment, the immunoglobulin variable region nucleotide sequence encodes an amino acid sequence that is at least 80%, at least 85%, at least 90%, at least 95%, or at least 98% identical with SEQ ID NO: 35. [000138] In one embodiment, the immunoglobulin variable region nucleotide sequence is at least 80%, at least 85%, at least 90%, at least 95%, or at least 98% identical with a human VH1 2 gene segment. In a specific embodiment, the immunoglobulin variable region nucleotide sequence is at least 80%, at least 85%, at least 90%, at least 95%, or at least 98% identical with SEQ ID NO: 60. In various embodiments, the human VH1-2 gene segment is identified from Table 3. [000139] In one embodiment, the immunoglobulin variable region nucleotide sequence encodes an amino acid sequence that is at least 80%, at least 85%, at least 90%, at least 95%, or at least 98% identical with SEQ ID NO: 61. [000140] In one aspect, use of a mouse as described herein to make a fully human Fab or a fully human F(ab) 2 is provided. In one embodiment, the fully human Fab or fully human F(ab)2 23 LJGKT 040. '11 U/A-VVU comprises a heavy chain variable region that comprises a rearranged human VH1-69 gene segment. In one embodiment, the fully human Fab or fully human F(ab)2 comprises a heavy chain variable region that comprises a rearranged human VH1- 2 gene segment. [000141] In one aspect, use of a mouse as described herein to make an immortalized cell line is provided. [000142] In one aspect, use of a mouse as described herein to make a hybridoma or quadroma is provided. [000143] In one aspect, use of a mouse as described herein to make a phage library containing human heavy chain variable regions and human light chain variable regions is provided. [000144] In one embodiment, the human heavy chain variable regions are derived from a human VH1 -69 gene segment that comprises a sequence selected from SEQ ID NO: 34, SEQ ID NO: 36, SEQ ID NO: 38, SEQ ID NO: 40, SEQ ID NO: 42, SEQ ID NO: 44, SEQ ID NO: 46, SEQ ID NO: 48, SEQ ID NO: 50, SEQ ID NO: 52, SEQ ID NO: 54, SEQ ID NO: 56 and SEQ ID NO: 58. [000145] In one embodiment, the human heavy chain variable regions are derived from a human VH1-69 gene segment that comprises a sequence selected from SEQ ID NO: 35, SEQ ID NO: 37, SEQ ID NO: 39, SEQ ID NO: 41, SEQ ID NO: 43, SEQ ID NO: 45, SEQ ID NO: 47, SEQ ID NO: 49, SEQ ID NO: 51, SEQ ID NO: 53, SEQ ID NO: 55, SEQ ID NO: 57 and SEQ ID NO: 59. [000146] In one embodiment, the human heavy chain variable regions are all derived from a human VH1- 2 gene segment that comprises a sequence selected from SEQ ID NO: 60, SEQ ID NO: 62, SEQ ID NO: 64, SEQ ID NO: 66 and SEQ ID NO: 68. [000147] In one embodiment, the human heavy chain variable regions are derived from a human VH1 -2 gene segment that comprises a sequence selected from SEQ ID NO: 61, SEQ ID NO: 63, SEQ ID NO: 65, SEQ ID NO: 67 and SEQ ID NO: 69. [000148] In one aspect, use of a mouse as described herein to generate a variable region sequence for making a human antibody is provided, comprising (a) immunizing a mouse as described herein with an antigen of interest, (b) isolating a lymphocyte from the immunized mouse of (a), (c) exposing the lymphocyte to one or more labeled antibodies, (d) identifying a lymphocyte that is capable of binding to the antigen of interest, and (e) amplifying one or more variable region nucleic acid sequence from the lymphocyte thereby generating a variable region sequence. [000149] In one embodiment, the lymphocyte is derived or isolated from the spleen of the mouse. In one embodiment, the lymphocyte is derived or isolated from a lymph node of the mouse. In one embodiment, the lymphocyte is derived or isolated from the bone marrow of the mouse. In one embodiment, the lymphocyte is derived or isolated from the blood of the mouse. 24 UOCKT N1O. 'JIU/M-VVUJ [000150] In one embodiment, the labeled antibody is a fluorophore-conjugated antibody. In one embodiment, the one or more fluorophore-conjugated antibodies are selected from an IgM, an IgG, and/or a combination thereof. [000151] In one embodiment, the lymphocyte is a B cell. [000152] In one embodiment, the one or more variable region nucleic acid sequence comprises a heavy chain variable region sequence. In one embodiment, the one or more variable region nucleic acid sequence comprises a light chain variable region sequence. In a specific embodiment, the light chain variable region sequence is an immunoglobulin K light chain variable region sequence. In one embodiment, the one or more variable region nucleic acid sequence comprises a heavy chain and a x light chain variable region sequence. [000153] In one embodiment, use of a mouse as described herein to generate a heavy and a K light chain variable region sequence for making a human antibody is provided, comprising (a) immunizing a mouse as described herein with an antigen of interest, (b) isolating the spleen from the immunized mouse of (a), (c) exposing B lymphocytes from the spleen to one or more labeled antibodies, (d) identifying a B lymphocyte of (c) that is capable of binding to the antigen of interest, and (e) amplifying a heavy chain variable region nucleic acid sequence and a K light chain variable region nucleic acid sequence from the B lymphocyte thereby generating the heavy chain and K light chain variable region sequences. [000154] In one embodiment, use of a mouse as described herein to generate a heavy and a K light chain variable region sequence for making a human antibody is provided, comprising (a) immunizing a mouse as described herein with an antigen of interest, (b) isolating one or more lymph nodes from the immunized mouse of (a), (c) exposing B lymphocytes from the one or more lymph nodes to one or more labeled antibodies, (d) identifying a B lymphocyte of (c) that is capable of binding to the antigen of interest, and (e) amplifying a heavy chain variable region nucleic acid sequence and a K light chain variable region nucleic acid sequence from the B lymphocyte thereby generating the heavy chain and K light chain variable region sequences. [000155] In one embodiment, use of a mouse as described herein to generate a heavy and a K light chain variable region sequence for making a human antibody is provided, comprising (a) immunizing a mouse as described herein with an antigen of interest, (b) isolating bone marrow from the immunized mouse of (a), (c) exposing B lymphocytes from the bone marrow to one or more labeled antibodies, (d) identifying a B lymphocyte of (c) that is capable of binding to the antigen of interest, and (e) amplifying a heavy chain variable region nucleic acid sequence and a K light chain variable region nucleic acid sequence from the B lymphocyte thereby generating the heavy chain and K light chain variable region sequences. In various embodiments, the one or more labeled antibodies are selected from an IgM, an IgG, and/or a combination thereof. [000156] In various embodiments, the antigen of interest is a pathogen that afflicts human 25 UOCKeT NO. 1I(UA-VVU subjects including, e.g., a viral antigen. Exemplary viral pathogens include, e.g., mainly those of the families of Adenoviridae, bacteria Picornaviridae, Herpesviridae, Hepadnaviridae, Flaviviridae, Retroviridae, Orthomyxoviridae, Paramyxoviridae, Papovaviridae, Polyomavirus, Rhabdoviridae, and Togaviridae. Such exemplary viruses typically range between 20-300 nanometers in length. In various embodiments, the antigen of interest is a viral antigen selected from a hepatitis virus (e.g., HCV, HBV, etc.), a human immunodeficiency virus (HIV), or an influenza virus (e.g., H1N1). [000157] In various embodiments, use of a mouse as described herein to generate a heavy and K light chain variable region sequence for making a human antibody is provided, further comprising fusing the amplified heavy and light chain variable region sequences to human heavy and light chain constant region sequences, expressing the fused heavy and light chain sequences in a cell, and recovering the expressed heavy and light chain sequences thereby generating a human antibody. [000158] In various embodiments, the human heavy chain constant regions are selected from IgM, IgD, IgA, IgE and IgG. In various specific embodiments, the IgG is selected from an IgG1, an IgG2, an IgG3 and an IgG4. In various embodiments, the human heavy chain constant region comprises a CH 1 , a hinge, a CH 2 , a CH 3 , a CH 4 , or a combination thereof. In various embodiments, the light chain constant region is an immunoglobulin K constant region. In various embodiments, the cell is selected from a HeLa cell, a DU145 cell, a Lncap cell, a MCF 7 cell, a MDA-MB-438 cell, a PC3 cell, a T47D cell, a THP-1 cell, a U87 cell, a SHSY5Y (human neuroblastoma) cell, a Saos-2 cell, a Vero cell, a CHO cell, a GH3 cell, a PC12 cell, a human retinal cell (e.g., a PER.C6 TM cell), and a MC3T3 cell. In a specific embodiment, the cell is a CHO cell. [000159] In one aspect, a method for generating a reverse-chimeric rodent-human antibody specific against an antigen of interest is provided, comprising the steps of immunizing a mouse as described herein with the antigen, isolating at least one cell from the mouse producing a reverse-chimeric mouse-human antibody specific against the antigen, culturing at least one cell producing the reverse-chimeric mouse-human antibody specific against the antigen, and obtaining said antibody. [000160] In one embodiment, the reverse-chimeric mouse-human antibody comprises a human heavy chain variable domain fused with a mouse or rat heavy chain constant gene, and a human light chain variable domain fused with a mouse or rat or human light chain constant gene. In a specific embodiment, the human heavy chain variable domain contains a rearranged human VH1-69 or human VH1-2 gene segment. [000161] In one embodiment, culturing at least one cell producing the reverse-chimeric rodent-human antibody specific against the antigen is performed on at least one hybridoma cell 26 UoCKe1 IMO. 'I4 1 U/A-VVV generated from the at least one cell isolated from the mouse. [000162] In one embodiment, the antigen of interest is a pathogen that afflicts human subjects as described herein. [000163] In one aspect, a method for generating a fully human antibody specific against an antigen of interest is provided, comprising the steps of immunizing a mouse as described herein with the antigen, isolating at least one cell from the mouse producing a reverse-chimeric rodent-human antibody specific against the antigen, generating at least one cell producing a fully human antibody derived from the reverse-chimeric rodent-human antibody specific against the antigen, and culturing at least one cell producing the fully human antibody, and obtaining said fully human antibody. [000164] In various embodiments, the at least one cell isolated from the mouse producing a reverse-chimeric rodent-human antibody specific against the antigen is a splenocyte or a B cell. [000165] In various embodiments, the antibody is a monoclonal antibody. [000166] In various embodiments, the antibody comprises a heavy chain variable domain that contains a rearranged human VH1-69 or human VH1-2 gene segment. [000167] In various embodiments, immunization with the antigen of interest is carried out with protein, DNA, a combination of DNA and protein, or cells expressing the antigen. In one embodiment, the antigen of interest is a pathogen that afflicts human subjects as described herein. [000168] In one aspect, use of a mouse as described herein to make a nucleic acid sequence encoding an immunoglobulin variable region or fragment thereof is provided. In one embodiment, the nucleic acid sequence is used to make a human antibody or antigen-binding fragment thereof. In one embodiment, the mouse is used to make an antigen-binding protein selected from an antibody, a multi-specific antibody (e.g., a bi-specific antibody), an scFv, a bi specific scFv, a diabody, a triabody, a tetrabody, a V-NAR, a VHH, a VL, a F(ab), a F(ab) 2 , a DVD (i.e., dual variable domain antigen-binding protein), a an SVD (i.e., single variable domain antigen-binding protein), or a bispecific T-cell engager (BiTE). [000169] In one aspect, a method for making a human antigen-binding protein is provided, comprising exposing a genetically modified non-human animal as described herein to an antigen of interest, allowing the genetically modified non-human animal to mount an immune response to the antigen, obtaining from the genetically modified non-human animal a heavy chain variable domain nucleic acid sequence encoding a human heavy chain variable domain that specifically binds the antigen of interest, cloning the heavy chain variable domain nucleic acid sequence to a human constant region sequence, and expressing in a mammalian cell an antibody comprising the human heavy chain variable domain sequence and the human constant region sequence. In one embodiment, the mammalian cell is a CHO cell. In one embodiment the genetically modified non-human animal comprises a human VH gene segment 27 JOCKel PAU. -I aIUM-VVU repertoire that consists essentially of a single human VH gene segment, optionally present in two or more polymorphic variants thereof, operably linked to one or more human D and/or J segments. In one embodiment, the human VH gene segment repertoire is at an endogenous non-human VH segment locus. In one embodiment, the human VH gene segment repertoire is at a locus that is not an endogenous VH segment locus. In one embodiment, the human VH gene segment rearranges with a human D segment and a human J segment to form a rearranged human VDJ gene operably linked to a constant region sequence, wherein the constant region sequence is selected from a human sequence and a rodent sequence (e.g., a mouse or rat or hamster sequence). In one embodiment, the constant region sequence comprises a sequence selected from a CH1, a hinge, a CH 2 , a CH 3 , and a combination thereof; in a specific embodiment, the constant region sequence comprises a CHI, a hinge, a CH2, and a CH 3 . In one embodiment, the human variable domain and the constant sequence are expressed in the mammalian cell with a cognate human light chain variable domain obtained from the same mouse (e.g., sequence obtained from the same B cell as the human variable domain sequence); in one embodiment the sequence encoding the human light chain variable domain obtained from the mouse is then fused with a sequence encoding a human light chain constant sequence, and the light chain sequence and the heavy chain sequence are expressed in the mammalian cell. [000170] In one embodiment, the antigen of interest is a pathogen that afflicts human subjects as described herein. [000171] In one aspect, a method for making an antibody heavy chain variable domain that binds an antigen of interest is provided, comprising expressing in a single cell (a) a first VH sequence of an immunized non-human animal as described herein, wherein the first VH sequence is fused with a CH gene sequence; and (b) a VL gene sequence of an immunized non-human animal as described herein, wherein the VL gene sequence is fused with a human CL gene sequence; maintaining the cell under conditions sufficient to express an antibody; and, isolating the antibody heavy chain variable domain. In one embodiment, the VL gene sequence is cognate with the first VH sequence. [000172] In one embodiment, the cell comprises a second VH gene sequence of an immunized non-human animal as described herein, wherein the second VH gene sequence is fused with a CH gene sequence, wherein the first VH gene sequence encodes a VH domain that specifically binds a first epitope, and the second VH gene sequence encodes a VH domain that specifically binds a second epitope, wherein the first epitope and the second epitope are not identical. [000173] In one embodiment, the constant region sequences are all human constant region sequences. In one embodiment, the antigen of interest is a pathogen that afflicts human subjects as described herein. 28 uoCKet ro. 1m1UA-VVU [000174] In one aspect, a method for making a human bispecific antibody is provided, comprising making the bispecific antibody using human variable region gene sequences of B cells of a non-human animal as described herein. [000175] In one embodiment, the method comprises (a) identifying a clonally selected lymphocyte of the non-human animal, wherein the non-human animal has been exposed to an antigen of interest and allowed to develop an immune response to the antigen of interest, and wherein the lymphocyte expresses an antibody that specifically binds the antigen of interest, (b) obtaining from the lymphocyte or the antibody a nucleotide sequence that encodes a human heavy chain variable region that specifically binds the antigen of interest, and (c) employing the nucleotide sequence that encodes the human heavy chain variable region that specifically binds the antigen of interest in making the bispecific antibody. In a specific embodiment, the human heavy chain variable region comprises a rearranged VH1-2 or VH1-69 gene segment. [000176] In one embodiment, steps (a) through (c) are performed a first time for a first antigen of interest to generate a first human heavy chain variable region sequence, and steps (a) through (c) are performed a second time for a second antigen of interest to generate a second human heavy chain variable region sequence, and wherein the first human heavy chain variable region sequence is expressed fused with a first human heavy chain constant region to form a first human heavy chain, the second human heavy chain variable region sequence is expressed fused with a second human heavy chain constant region to form a second human heavy chain, wherein the first and the second human heavy chains are expressed in the presence of a single human light chain expressed from a rearranged human V1 -39 or a human VK3-20 gene segment. In a specific embodiment, the single human light chain comprises a germline sequence. [000177] In one embodiment, the method comprises (a) cloning heavy chain variable regions from B cells of a non-human animal as described herein which has been exposed to a first antigen of interest, and the same non-human animal, or a different non-human animal which is genetically the same and has been exposed to a second antigen of interest; and (b) expressing in a cell the heavy chain variable regions of (a) with the same heavy chain constant region and the same light chain to make a bispecific antibody. [000178] In one aspect, a use of a non-human animal as described herein is provided, to obtain a nucleic acid sequence that encodes a human heavy chain variable domain. In one embodiment, the heavy chain variable domain comprises a rearranged human VH gene segment selected from VH1-2 and VH1-69. [000179] In one aspect, a use of a non-human animal as described herein is provided, to obtain a cell that encodes a human heavy chain variable domain. In one embodiment, the heavy chain variable domain comprises a rearranged human VH gene segment selected from 29 LJOCKet 14O. 'I/UIAM-VVI VH1-2 and VH1-69. [000180] In one aspect, use of a non-human animal as described herein to make a human antibody variable domain is provided. In one embodiment, the variable domain comprises a rearranged human VH gene segment selected from VH1- 2 and VH1- 6 9 . [000181] In one aspect, use of a non-human animal as described herein to make a human antibody is provided, comprising making the antibody using human variable region gene sequences of B cells of a non-human animal as described herein. In one embodiment, the human antibody is a human bispecific antibody. In a specific embodiment, the bispecific antibody comprises one heavy chain variable domain derived from a rearranged human VH1-2 or VH1 -69 gene segment. In one embodiment, the human variable region gene sequences comprise a rearranged human VH1-2 or VH1-69 gene segment. [000182] In one aspect, use of a non-human animal as described herein is provided to select a human immunoglobulin heavy chain variable domain. In one embodiment, the heavy chain variable domain comprises a rearranged human VH gene segment selected from VH1-2 and

VH

1

-

6 9 [000183] In one aspect, use of the mouse as described herein for the manufacture of a medicament (e.g., an antigen-binding protein), or for the manufacture of a sequence encoding a variable sequence of a medicament (e.g., an antigen-binding protein), for the treatment of a human disease or disorder is provided. In one embodiment, the variable sequence of a medicament comprises a polymorphic human VH gene segment. In one embodiment, the variable sequence of a medicament comprises a human VH1-69 gene segment. In one embodiment, the variable sequence of a medicament comprises a human VH1-2 gene segment. [000184] In one aspect, a nucleic acid construct encoding an immunoglobulin variable domain made in a mouse as described herein is provided. In one embodiment, the variable domain is a heavy chain variable domain. In a specific embodiment, the heavy chain variable domain comprises a rearranged human VH gene segment selected from VH1- 2 , VH1- 6 9 , VH2-26, VH2 70, or VH3-23. In another specific embodiment, the heavy chain variable domain comprises a rearranged human VH1-2 gene segment. In another specific embodiment, the heavy chain variable domain comprises a rearranged human VH1-69 gene segment. [000185] In one embodiment, the variable domain is a light chain variable domain. In a specific embodiment, the variable domain is a K light chain variable domain that is cognate with a human heavy chain variable domain that comprises a rearranged human VH1-69 gene segment. In a specific embodiment, the variable domain is a K light chain variable domain that is cognate with a human heavy chain variable domain that comprises a rearranged human VH1 2 gene segment. [000186] In one aspect, use of a mouse as described herein to make a nucleic acid construct 30 JOCKeT INo. '1JIU/-VVU encoding a human immunoglobulin variable domain is provided. In one embodiment, the variable domain is a light chain variable domain. In one embodiment, the variable domain is a K light chain variable domain that comprises a rearranged human VK gene segment selected from VK4-1, VK 5

-

2 , V7-3, VK2-4, VK1-5, Vi1-6, VK 3

-

7 , VK1- 8 , VK1-9, VK2-10, Vx3-11, VK1-1 2 , VKI-13, Vx2-14, VK 3 -1 5 , VK1-1 6 , VK1-17, VK 2 -1 8 , VK 2 -1 9 , VK3-20, VK 6

-

2 1, VK1- 2 2 , VI1- 2 3 , VK2-24, Vx 3

-

2 5 , VK 2

-

2 6 , V1-27, VK2-28, Vx2-29, VK2-30, VK3-31, V1-32, V1-33, Vx3-34, Vx1-35, VK2-36, Vxl-37, VK 2

-

3 8 , VK1-39, and VK 2

-

4 0. [000187] In one embodiment, the variable domain is a heavy chain variable domain. In a specific embodiment, the heavy chain variable domain comprises a rearranged human VH gene segment selected from VH1-2, VH1-69, VH2-26, VH2-70, or VH3-23. In a specific embodiment, the heavy chain variable domain comprises a rearranged human VH1-69 gene segment. In a specific embodiment, the heavy chain variable domain comprises a rearranged human VH1-2 gene segment. [000188] In one aspect, use of a mouse as described herein to make a human immunoglobulin variable domain is provided. In one embodiment, the variable domain is a light chain variable domain. In one embodiment, the variable domain is a K light chain variable domain that comprises a rearranged human VK gene segment selected from VK 4 -1, Vx5-2,

VK

7

-

3 , Vx 2

-

4 , V-1-5, Vx1- 6 , VK3-7, Vx1- 8 , VK1- 9 , VK2-10, Vx3-11, VK1-12, VO1-13, Vx2-14, Vx3-15, VK1-16, VK1-17, Vx2-18, Vx2-19, Vx3-20, VK6-21, Vx1-22, VK1-23, Vx2-24, Vx3-25, VK2-26, VK1-27, V12-28, Vx 2

-

2 9 , Vx2-30, Vx3-31, VK1-32, Vx1-33, VK3-34, VK1-35, Vx2-36, VK1-37, VK2-38, V1-39, and VK2-40. [000189] In one embodiment, the variable domain is a heavy chain variable domain. In a specific embodiment, the heavy chain variable domain comprises a rearranged human VH gene segment selected from VH1- 2 , VH1-69, VH2-26, VH 2

-

7 0, or VH 3

-

2 3 . In a specific embodiment, the heavy chain variable domain comprises a rearranged human VH1-69 gene segment. In a specific embodiment, the heavy chain variable domain comprises a rearranged human VH1-2 gene segment. [000190] In one aspect, use of a non-human animal as described herein to make a nucleic acid sequence encoding a human heavy chain variable domain is provided. In one embodiment, the human heavy chain variable domain is characterized by having human FR1 CDR1-FR2-CDR2-FR3 sequences that are derived from a polymorphic human VH gene segment. In a specific embodiment, the human VH gene segment is selected from a human VH1-2, VH1- 6 9 , VH2-26, VH2-70, or VH3-23 gene segment. In one embodiment, the human VH gene segment is a human VH1-69 gene segment. In one embodiment, the human VH gene segment is a human VH1- 2 gene segment. [000191] In one aspect, a method for making a nucleic acid sequence encoding a human VH 31 vOCKex No. 1,munA-VVU domain is provided, the method comprising immunizing a non-human animal as described herein with an antigen of interest, allowing the non-human animal to mount an immune response to the antigen of interest, and obtaining therefrom a nucleic acid sequence encoding a human VH domain that binds the antigen of interest. In one embodiment, the method further comprises making a nucleic acid sequence encoding a human VL domain that is cognate with the human VH domain, comprising isolating a B cell encoding the human VH domain and the human VL domain, and obtaining therefrom the sequence of the heavy and light chain variable domains. In various embodiments, the human VH domain is derived from a rearranged human VH1-69 or human VH1-2 gene segment. In various embodiments, the human VL domain is selected from a human VK or a human VX domain. [000192] In one aspect, use of a non-human animal as described herein to make a human therapeutic is provided, comprising immunizing the non-human animal with an antigen of interest, allowing the non-human animal to mount an immune response, and obtaining from the animal a nucleic acid sequence encoding an immunoglobulin variable domain that binds the antigen of interest, and employing the immunoglobulin variable domain in a human therapeutic. In one embodiment, the variable domain is a heavy chain variable domain. In a specific embodiment, the heavy chain variable domain is derived from a rearranged human VH1 -69 or a human VH1-2 gene segment. In one embodiment, the variable domain is a light chain variable domain. In a specific embodiment, the light chain variable domain is derived from a rearranged human VK or human VX gene segment. [000193] In one aspect, a method for making a human therapeutic is provided, comprising immunizing a non-human animal as described herein with an antigen of interest, allowing the non-human animal to mount an immune response, and obtaining from the animal a nucleic acid sequence encoding an immunoglobulin variable domain that binds the antigen of interest, and employing the immunoglobulin variable domain in a human therapeutic. In one embodiment, the variable domain is a heavy chain variable domain. In a specific embodiment, the heavy chain variable domain is derived from a rearranged human VH1 -69 or a human VH1-2 gene segment. In one embodiment, the variable domain is a light chain variable domain. In a specific embodiment, the light chain variable domain is derived from a rearranged human VK or human VX gene segment. [000194] In one aspect, a method for making a human antigen-binding protein is provided, comprising immunizing a non-human animal as described herein with an antigen of interest, allowing the animal to mount an immune response, obtaining from the mouse a nucleic acid sequence encoding an immunoglobulin variable domain that specifically binds the antigen of interest, cloning the nucleic acid sequence in a vector suitable for expression of the nucleic acid, wherein the nucleic acid sequence is cloned in frame with a nucleic acid sequence 32 UUCKeL 11O. 13I1V-VVUV encoding a human immunoglobulin constant region or functional fragment thereof, and inserting the vector in a mammalian cell, and maintaining the cell under conditions suitable for expressing an antigen-binding protein that comprises the immunoglobulin variable domain and the immunoglobulin constant region or functional fragment thereof. In one embodiment, the antigen-binding protein is a human antibody. In a specific embodiment, the antibody comprises a heavy chain variable domain and a light chain variable domain obtained from a mouse as described herein. In a specific embodiment, the antibody comprises a heavy chain variable domain obtained from a mouse as described herein. In various embodiments, the heavy chain variable domain is derived from a rearranged human VH1- 6 9 or a human VH1- 2 gene segment. [000195] In one aspect, a nucleic acid sequence encoding a human antigen-binding domain made in a non-human animal as described herein is provided. In one embodiment, the nucleic acid sequence encodes a human immunoglobulin VH domain. In one embodiment, the nucleic acid sequence encodes a human immunoglobulin VH domain and a cognate human VL domain. In various embodiments, the human VH domain is derived from a rearranged human VH1-69 or a human VH1-2 gene segment. [000196] In one aspect, a method for preparation of a human antibody is provided, comprising immunizing a non-human animal as described herein with an antigen of interest, allowing the non-human animal to mount an immune response, harvesting a lymphocyte (e.g., a B cell) from the immunized animal, fusing the lymphocyte with a myeloma cell to form a hybridoma cell, obtaining from the hybridoma cell a nucleic acid sequence that encodes a human VH domain and a human VL domain, cloning the nucleic acid sequence in frame (i.e., in operable linkage) with a human constant region sequence to create an immunoglobulin heavy chain and an immunoglobulin light chain, and expressing the heavy and light chains in a cell capable of expressing the fully human antibody. In one embodiment, the cell is a CHO cell. In various embodiments, the human VH domain is derived from a rearranged human VH1-69 gene segment or a human VH1-2 gene segment. [000197] In one aspect, a method for preparation of a human antibody is provided, comprising immunizing a non-human animal as described herein with an antigen of interest, allowing the non-human animal to mount an immune response, harvesting a lymphocyte (e.g., a B cell) from the immunized animal, obtaining from the lymphocyte a nucleic acid sequence that encodes a human VH domain and a human VL domain, cloning the nucleic acid sequence in frame (i.e., in operable linkage) with a human constant region sequence to create an immunoglobulin heavy chain and an immunoglobulin light chain, and expressing the heavy and light chains in a cell capable of expressing the fully human antibody. In one embodiment, the lymphocyte is derived from the spleen of the non-human animal. In one embodiment, the cell is a CHO cell. In various embodiments, the human VH domain is derived from a rearranged human VH1-69 gene segment or a human VH1-2 gene segment. 33 uoCKeO NO. 1W UA-VVU [000198] In various aspects, the antigen of interest is a pathogen that afflicts human subjects as described herein. In various aspects, the antigen of interest is a virus that is capable of infecting a human. Exemplary antigens that can be employed in the methods and uses described herein include microbes or microorganisms such as a virus, bacterium, prion, or fungus or any other pathogen that causes disease in humans. A person of skill, upon reading the disclosure, will appreciate those human pathogens that will be applicable for the methods and uses described herein. The various aspects and embodiments are capable of use together, unless expressly noted otherwise or the context clearly prohibits use together. BRIEF DESCRIPTION OF FIGURES [000199] FIG. I shows a general illustration, not to scale, of a series of targeting and molecular engineering steps employed to make a targeting vector for construction of a modified heavy chain locus containing a single human VH1 -69 gene segment, twenty-seven human DH and six human JH gene segments at an endogenous immunoglobulin heavy chain locus. [000200] FIG. 2 shows a general illustration, not to scale, of a series of targeting and molecular engineering steps employed to make a targeting vector for construction of a modified heavy chain locus containing a single human VH1-2 gene segment, twenty-seven human DH and six human JH gene segments at an endogenous immunoglobulin heavy chain locus. [000201] FIG. 3 shows contour plots of splenocytes gated on single lymphocytes and stained for CD1 9 (B cell) and CD3 (T cell) from a wild type mouse (WT) and a mouse homozygous for a single human VH gene segment, twenty-seven human DH and six human JH gene segments at the endogenous immunoglobulin heavy chain locus (IhVH HO). [000202] FIG. 4A shows, on the left, the percent of CD19' B cells in spleens harvested from wild type mice (WT) and mice homozygous for a single human VH gene segment, twenty-seven human DH and six human JH gene segments at the endogenous immunoglobulin heavy chain locus (1hVH HO). On the right, the number of CD19* B cells per spleen is shown for both wild type mice (WT) and mice homozygous for a single human VH gene segment, twenty-seven human DH and six human JH gene segments at the endogenous immunoglobulin heavy chain locus (1 hVH HO). [000203] FIG. 4B shows, on the left, the percent of CD19* B cells in bone marrow harvested from femurs of wild type mice (WT) and mice homozygous for a single human VH gene segment, twenty-seven human DH and six human JH gene segments at the endogenous immunoglobulin heavy chain locus (1hVH HO). On the right, the number of CD19* B cells per femur is shown for both wild type mice (WT) and mice homozygous for a single human VH gene segment, twenty-seven human DH and six human JH gene segments at the endogenous immunoglobulin heavy chain locus (1hVH HO). 34 IJOCliI INO. 'IIUA-V'VVU [000204] FIG. 5 shows contour plots of splenocytes gated on CD19* B cells and stained for lgk+ and igK+ expression from a wild type mouse (WT) and a mouse homozygous for a single human VH gene segment, twenty-seven human DH and six human JH gene segments at the endogenous immunoglobulin heavy chain locus (1hVH HO). [000205] FIG. 6 shows contour plots of splenocytes gated on CD19* B cells and stained for immunoglobulin D (IgD) and immunoglobulin M (IgM) from a wild type mouse (WT) and a mouse homozygous for a single human VH gene segment, twenty-seven human DH and six human JH gene segments at the endogenous immunoglobulin heavy chain locus (1 hVH HO). [000206] FIG. 7 shows the total number of transitional B cells (CD19'lgMhilgDnt), mature B cells (CD19'IgMintlgDhi), and the ratio of mature to immature B cells in harvested spleens from wild type mice (WT) and mice homozygous for a single human VH gene segment, twenty-seven human DH and six human JH gene segments at the endogenous immunoglobulin heavy chain locus (1hVH HO). [000207] FIG. 8 shows contour plots of bone marrow gated on singlets stained for immunoglobulin M (IgM) and B220 from a wild type mouse (WT) and a mouse homozygous for a single human VH gene segment, twenty-seven human DH and six human JH gene segments at the endogenous immunoglobulin heavy chain locus (1 hVH HO). [000208] FIG. 9 shows the total number of immature (B220ntigM+) and mature (B220hilgM+) B cells in bone marrow isolated from the femurs of wild type mice (WT) and mice homozygous for a single human VH gene segment, twenty-seven human DH and six human JH gene segments at the endogenous immunoglobulin heavy chain locus (1 hVH HO). [000209] FIG. 10 shows contour plots of bone marrow gated on CD19* B cells and stained for ckit* and CD43* from a wild type mouse (WT) and a mouse homozygous for a single human VH gene segment, twenty-seven human DH and six human JH gene segments at the endogenous immunoglobulin heavy chain locus (1hVH HO). [000210] FIG. 11A shows the percent of CD19* cells in populations of pro B (CD19*CD43*ckit*) and pre B (CD1 9'CD43-ckit-) cells in bone marrow harvested from the femurs of wild type mice (WT) and mice homozygous for a single human VH gene segment, twenty-seven human DH and six human JH gene segments at the endogenous immunoglobulin heavy chain locus (1hVH HO). [000211] FIG. 11B shows the absolute number of cells per femur in populations of pro B (CD19'CD43*ckit*) and pre B (CD19*CD43-ckit-) cells in bone marrow harvested from wild type mice (WT) and mice homozygous for a single human VH gene segment, twenty-seven human DH and six human JH gene segments at the endogenous immunoglobulin heavy chain locus (1hVH HO). [000212] FIG. 12 shows the relative mRNA expression (y-axis) in purified splenic B cells of VH1-69-derived heavy chains in a quantitative PCR assay using a probe specific for the human 35 uOCKe. INO. 'i3aUA-VVU VH1-69 gene segment in mice homozygous for a replacement of the endogenous heavy chain VH, DH, JH, and a replacement of the endogenous light chain Vic and JK gene segments with human VH, DH, JH, Vi and Ji< gene segments (Hic), wild type mice (WT), mice heterozygous for a single human VH gene segment, twenty-seven human DH and six human JH gene segments at the endogenous immunoglobulin heavy chain locus (1 hVH HET) and mice homozygous for a single human VH gene segment, twenty-seven human DH and six human JH gene segments at the endogenous immunoglobulin heavy chain locus (1hVH HO). Signals are normalized to expression of mouse CK. [000213] FIG. 13 shows the nucleotide alignment of the second exon for each of thirteen reported alleles for the human VH1-69 gene. Lower case bases indicate germline nucleotide differences among the alleles. Complementary determining regions (CDRs) are indicated with boxes around the sequence. Dashes indicate artificial gaps for proper sequence alignment. VH1-69*01 (SEQ ID NO: 34); VH1-69*02 (SEQ ID NO: 36); VH1-69*03 (SEQ ID NO: 38); VH1 69*04 (SEQ ID NO: 40); VH1-69*05 (SEQ ID NO: 42); VH1-69*06 (SEQ ID NO: 44); VH1-69*07 (SEQ ID NO: 46); VH1-69*08 (SEQ ID NO: 48); VH1- 6 9 *0 9 (SEQ ID NO: 50); VH1-69*10 (SEQ ID NO: 52); VH1-69*11 (SEQ ID NO: 54); VHI-69*12 (SEQ ID NO: 56); VH1-69*13 (SEQ ID NO: 58). [000214] FIG. 14 shows the protein alignment of the mature heavy chain variable gene sequence for each of thirteen reported alleles for the human VH1-69 gene. Lower case amino acids indicate germline differences among the alleles. Complementary determining regions (CDRs) are indicated with boxes around the sequence. Dashes indicate artificial gaps for proper sequence alignment. VHI-69*01 (SEQ ID NO: 35); VH1-69*02 (SEQ ID NO: 37); VH1 69*03 (SEQ ID NO: 39); VH1-69*04 (SEQ ID NO: 41); VH1-69*05 (SEQ ID NO: 43); VH1-69*06 (SEQ ID NO: 45); VH1- 6 9 *0 7 (SEQ ID NO: 47); VH1-69*08 (SEQ ID NO: 49); VH1- 6 9 *0 9 (SEQ ID NO: 51); VH1-69*10 (SEQ ID NO: 53); VH1-69*11 (SEQ ID NO: 55); VH1-69*12 (SEQ ID NO: 57); VH1-69*1 3 (SEQ ID NO: 59). [000215] FIG. 15 shows a percent identity/percent similarity matrix for the aligned protein sequences of the mature variable gene for each of thirteen reported alleles for the human VH1 69 gene. Percent identity among the VH1- 6 9 alleles is indicated above the shaded boxes and percent similarity is indicated below the shaded boxes. Scores for percent identity and percent similarity were scored by a ClustaIW (v1.83) alignment tool using MacVector software (MacVector, Inc., North Carolina). [000216] FIG. 16 shows the nucleotide alignment of the second exon for each of five reported alleles for the human VH1-2 gene. Lower case bases indicate germline nucleotide differences among the alleles. Complementary determining regions (CDRs) are indicated with boxes around the sequence. Dashes indicate artificial gaps for proper sequence alignment. VH1-2*01 36 UOCKet NO. 1J(UA-VVU (SEQ ID NO: 60); VH1-2*02 (SEQ ID NO: 62); VH1-2*03 (SEQ ID NO: 64); VH1-2*04 (SEQ ID NO: 66); VH1-2*05 (SEQ ID NO: 68). [000217] FIG. 17 shows the protein alignment of the mature heavy chain variable gene sequence for each of five reported alleles for the human VH1-2 gene. Lower case amino acids indicate germline differences among the alleles. Complementary determining regions (CDRs) are indicated with boxes around the sequence. Dashes indicate artificial gaps for proper sequence alignment. VH1-2*01 (SEQ ID NO: 61); VH1-2*02 (SEQ ID NO: 63); VH1-2*03 (SEQ ID NO: 65); VH1-2*04 (SEQ ID NO: 67); VH1-2*05 (SEQ ID NO: 69). [000218] FIG. 18 shows a percent identity/percent similarity matrix for the aligned protein sequences of the mature variable gene for each of five reported alleles for the human VH1 -2 gene. Percent identity among the VHI-2 alleles is indicated above the shaded boxes and percent similarity is indicated below the shaded boxes. Scores for percent identity and percent similarity were scored by a ClustalW (v1.83) alignment tool using MacVector software (MacVector, Inc., North Carolina). [000219] FIG. 19 shows the antibody titer from mice homozygous for human heavy and human K light chain variable gene loci (HK; n=4) and mice homozygous for a single human VHl 69 gene segment, twenty-seven human DH and six human JH gene segments at the endogenous immunoglobulin heavy chain locus (1hVHHO; n=10) that were immunized with a human cell surface receptor (Antigen A). [000220] FIG. 20 shows the antibody titer from mice homozygous for human heavy and human K light chain variable gene loci (HK; n=5) and mice homozygous for a single human VH1 69 gene segment, twenty-seven human DH and six human JH gene segments at the endogenous immunoglobulin heavy chain locus (1hVHHO; n=5) that were immunized with two different influenza vaccines. [000221] FIG. 21 shows the percentage (y-axis) of IgM-primed heavy chains having a specified amino acid length for the VH CDR3 region (x-axis) from mice homozygous for a single human VHi -69 gene segment, twenty-seven human DH and six human JH gene segments at the endogenous immunoglobulin heavy chain locus and homozygous for a replacement of the endogenous K light chain variable loci with human K light chain variable loci that were immunized with a human cell surface receptor (Antigen A). [000222] FIG. 22 shows the percentage (y-axis) of IgG-primed heavy chains having a specified amino acid length for the VH CDR3 region (x-axis) from mice homozygous for a single human VHi-69 gene segment, twenty-seven human DH and six human JH gene segments at the endogenous immunoglobulin heavy chain locus and homozygous for a replacement of the endogenous K light chain variable loci with human K light chain variable loci that were immunized with a human cell surface receptor (Antigen A). 37 UOCKet ro. '1iUA-VVU DETAILED DESCRIPTION [000223] This invention is not limited to particular methods, and experimental conditions described, as such methods and conditions may vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting, since the scope of the present invention is defined by the claims. [000224] Unless defined otherwise, all terms and phrases used herein include the meanings that the terms and phrases have attained in the art, unless the contrary is clearly indicated or clearly apparent from the context in which the term or phrase is used. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, particular methods and materials are now described. All publications mentioned are hereby incorporated by reference. [000225] The phrase "substantial" or "substantially" when used to refer to an amount of gene segments (e.g., "substantially all" V gene segments) includes both functional and non functional gene segments and include, in various embodiments, e.g., 80% or more, 85% or more, 90% or more, 95% or more 96% or more, 97% or more, 98% or more, or 99% or more of all gene segments; in various embodiments, "substantially all" gene segments includes, e.g., at least 95%, 96%, 97%, 98%, or 99% of functional (i.e., non-pseudogene) gene segments. [000226] The term "replacement" includes wherein a DNA sequence is placed into a genome of a cell in such a way as to replace a sequence within the genome with a heterologous sequence (e.g., a human sequence in a mouse), at the locus of the genomic sequence. The DNA sequence so placed may include one or more regulatory sequences that are part of source DNA used to obtain the sequence so placed (e.g., promoters, enhancers, 5'- or 3' untranslated regions, appropriate recombination signal sequences, etc.). For example, in various embodiments, the replacement is a substitution of an endogenous sequence for a heterologous sequence that results in the production of a gene product from the DNA sequence so placed (comprising the heterologous sequence), but not expression of the endogenous sequence; the replacement is of an endogenous genomic sequence with a DNA sequence that encodes a protein that has a similar function as a protein encoded by the endogenous genomic sequence (e.g., the endogenous genomic sequence encodes an immunoglobulin gene or domain, and the DNA fragment encodes one or more human immunoglobulin genes or domains). In various embodiments, an endogenous gene or fragment thereof is replaced with a corresponding human gene or fragment thereof. A corresponding human gene or fragment thereof is a human gene or fragment that is an ortholog of, a homolog of, or is substantially identical or the same in structure and/or function, as the endogenous gene or fragment thereof that is replaced. [000227] A precise, in situ replacement of six megabases of the variable regions of the mouse 38 uoCKeT NO. 1JIUA-VVU heavy chain immunoglobulin loci (VH-DH-JH) with a restricted human immunoglobulin heavy chain locus was performed, while leaving the flanking mouse sequences intact and functional within the hybrid loci, including all mouse constant chain genes and locus transcriptional control regions (FIG. 1 and FIG. 2). Specifically, a single human VH, 27 DH, and six JH gene segments were introduced through chimeric BAC targeting vectors into mouse ES cells using VELOCIGENE@ genetic engineering technology (see, e.g., US Pat. No. 6,586,251 and Valenzuela et al., 2003, High-throughput engineering of the mouse genome coupled with high resolution expression analysis, Nat Biotechnol 21:652-659). Non-Human Animals With Restricted Immunoglobulin VH Gene Segments [000228] Non-human animals comprising immunoglobulin loci that comprise a restricted number of VH genes, and one or more D genes and one or more J genes, are provided, as are methods of making and using them. When immunized with an antigen of interest, the non human animals generate B cell populations with antibody variable regions derived only from the restricted, pre-selected VH gene or set of VH genes (e.g., a pre-selected VH gene and variants thereof). In various embodiments, non-human animals are provided that generate B cell populations that express human antibody variable domains that are human heavy chain variable domains, along with cognate human light chain variable domains. In various embodiments, the non-human animals rearrange human heavy chain variable gene segments and human light chain variable gene segments from modified endogenous mouse immunoglobulin loci that comprise a replacement or insertion of the non-human unrearranged variable region sequences with human unrearranged variable region sequences. [000229] Early work on the organization, structure, and function of the immunoglobulin genes was done in part on mice with disabled endogenous loci and engineered to have transgenic loci (randomly placed) with partial human immunoglobulin genes, e.g., a partial repertoire of human heavy chain genes linked with a human constant gene, randomly inserted into the genome, in the presence or absence of a human light chain transgene. Although these mice were somewhat less than optimal for making useful high affinity antibodies, they facilitated certain functional analyses of immunoglobulin loci. Some of these mice had as few as two or three, or even just a single, heavy chain variable gene. [000230] Mice that express fully human immunoglobulin heavy chains derived from a single human VH5-51 gene and 10 human DH genes and six human JH genes, with human p. and yl constant genes, on a randomly inserted transgene (and disabled endogenous immunoglobulin loci) have been reported (Xu and Davis, 2000, Diversity in the CDR3 Region of VH Is Sufficient for Most Antibody Specificities, Immunity 13:37-45). The fully human immunoglobulin heavy chains of these mice are mostly expressed with one of just two fully mouse k light chains 39 IJOGKII MO. I Of UMI-VVid derived from the endogenous mouse X light chain locus (VX1-Jk1 or Vk2-Jk2 only), and can express no K light chain (the mice are Igx'). These mice exhibit severely abnormal dysfunction in B cell development and antibody expression. B cell numbers are reportedly 5-10% of wild type, IgM levels 5-10% of wild-type, and IgG1 levels are only 0.1-1% of wild-type. The observed IgM repertoire revealed highly restricted junctional diversity. The fully human heavy chains display largely identical CDR3 length across antigens, the same JH (JH2) usage across antigens, and an initial junctional Q residue, thus reflecting a certain lack of CDR3 diversity. The fully mouse k light chains nearly all had a W96L substitution in Jk1 as initial junctional residue. The mice are reportedly unable to generate any antibodies against bacterial polysaccharide. Because the human variable domains couple with mouse light chains, the utility of the human variable regions is highly limited. [000231] Other mice that have just a single human VH 3

-

2 3 gene, human DH and JH genes, and mouse light chain genes have been reported, but they exhibit a limited diversity (and thus a limited usefulness) due in part to mispairing potential between human VH and mouse VL domains (see, e.g., Mageed et al., 2001, Rearrangement of the human heavy chain variable region gene V3-23 in transgenic mice generates antibodies reactive with a range of antigens on the basis of VHCDR3 and residues intrinsic to the heavy chain variable region, Clin. Exp. Immunol. 123:1-5). Similarly, mice that bear two VH genes (3-23 and 6-1) along with human DH and JH genes in a transgene containing the human p constant gene (Bruggemann et al., 1991, Human antibody production in transgenic mice: expression from 100kb of the human IgH locus, Eur. J. lmmmunol. 21:1323-1326) and express them in human IgM chains with mouse light chains may exhibit a repertoire limited by mispairing (Mackworth-Young et al., 2003, The role of antigen in the selection of the human V3-23 immunoglobulin heavy chain variable region gene, Clin. Exp. Immunol. 134:420-425). [000232] Other transgenic mice that express VH-restricted fully human heavy chains from a human transgene randomly inserted in the genome, with a limited human k repertoire expressed from a fully human randomly inserted transgene, have also been reported (see, e.g., Taylor et al., 1992, A transgenic mouse that expresses a diversity of human sequence heavy and light chain immunoglobulins, Nucleic Acids Res. 20(23):6287-6295; Wagner et al., 1994, Antibodies generated form human immunoglobulin miniloci in transgenic mice, Nucleic Acids Res. 22(8):1389-1393). However, transgenic mice that express fully human antibodies from transgenes randomly integrated into the mouse genome, and that comprise damaged endogenous loci, are known to exhibit substantial differences in immune response as compared with wild-type mice that affect the diversity of the antibody variable domains obtainable from such mice. 40 UOCKei WO. I3IUA-VVU [000233] Useful non-human animals that generate a diverse population of B cells that express human antibody variable domains from a restricted VH gene repertoire and one or more D genes and one or more J genes will be capable of generating, preferably in some embodiments, repertoires of rearranged variable region genes that will be sufficiently diverse. In various embodiments, diversity includes junctional diversity, somatic hypermutation, and polymorphic diversity in VH gene sequence (for embodiments where VH genes are present in polymorphic forms). Combinatorial diversity occurs in the pairing of the VH gene with one of a plurality of cognate human light chain variable domains (which, in various embodiments, comprise junctional diversity and/or somatic hypermutations). [000234] Non-human animals comprising a restricted human VH gene repertoire and a complete or substantially complete human VL gene repertoire will in various embodiments generate populations of B cells that reflect the various sources of diversity, such as junctional diversity (e.g., VDJ, VJ joining, P additions, N additions), combinatorial diversity (e.g., cognate VH-restricted human heavy, human light), and somatic hypermutations. In embodiments comprising a restriction of the VH repertoire to one human VH gene, the one human VH gene can be present in two or more variants. In various embodiments, the presence of two or more polymorphic forms of a VH gene will enrich the diversity of the variable domains of the B cell population. [000235] Variations in the germline sequences of gene segments (e.g., V genes) contribute to the diversity of the antibody response in humans. The relative contribution to diversity due to V gene sequence differences varies among V genes. The degree of polymorphism varies across gene families, and is reflected in a plurality of haplotypes (stretches of sequence with coinherited polymorphisms) capable of generating further diversity as observed in VH haplotype differences between related and unrelated individuals in the human population (see, e.g., Souroujon et al., 1989, Polymorphisms in Human H Chain V Region Genes from the VHIII Gene Family, J. Immunol. 143(2):706-711). Some have suggested, based on data from particularly polymorphic human VH gene families, that haplotype diversity in the germline is a major contributor to VH gene heterogeneity in the human population, which is reflected in the large diversity of different germline VH genes across the human population (see, Sasso et al., 1990, Prevalence and Polymorphism of Human VH3 Genes, J. Immunol. 145(8):2751-2757). [000236] Although the human population displays a large diversity of haplotypes with respect to the VH gene repertoire due to widespread polymorphism, certain polymorphisms are reflected in prevalent (i.e., conserved) alleles observed in the human population (Sasso et al., 1990). VH polymorphism can be described in two principle forms. The first is variation arising from allelic variation associated with differences among the nucleotide sequence between alleles of the same gene segment. The second arises from the numerous duplications, insertions, and/or deletions that have occurred at the immunoglobulin heavy chain locus. This 41 vOCKet ro. 15 VA-VVu has resulted in the unique situation in which VH genes derived by duplication from identical genes differ from their respective alleles by one or more nucleotide substitutions. This also directly influences the copy number of VH genes at the heavy chain locus. [000237] Polymorphic alleles of the human immunoglobulin heavy chain variable gene segments (VH genes) have largely been the result of insertion/deletion of gene segments and single nucleotide differences within coding regions, both of which have the potential to have functional consequences on the immunoglobulin molecule. Table 1 sets forth the functional VH genes listed by human VH gene family and the number of identified alleles for each VH gene in the human immunoglobulin heavy chain locus. There are some findings to suggest that polymorphic VH genes have been implicated in susceptibility to certain diseases such as, for example, rheumatoid arthritis, whereas in other cases a linkage between VH and disease has been less clear. This ambiguity has been attributed to the copy number and presence of various alleles in different human populations. In fact, several human VH genes demonstrate copy number variation (e.g., VHI-2, VH1-69, VH2-26, VH2-70, and VH3-23). In various embodiments, humanized mice as described herein with restricted VH repertoires comprise multiple polymorphic variants of an individual VH family member (e.g., two or more polymorphic variants of VH1 -2, VH1 -69, VH2-26, VH2-70, or VH3-23, replacing all or substantially all functional mouse VH segments at an endogenous mouse locus). In a specific embodiment, the two or more polymorphic variants of mice described herein are in number up to and including the number indicated for the corresponding VH family member in Table 1 (e.g., for VH1-69, 13 variants; for VH1-2, five variants; etc.). [000238] Commonly observed variants of particular human VH genes are known in the art. For example, one of the most complex polymorphisms in the VH locus belongs to the VH1-69 gene. The human VHI-69 gene has 13 reported alleles (Sasso et al., 1993, A fetally expressed immunoglobulin VH1 gene belongs to a complex set of alleles, Journal of Clinical Investigation 91:2358-2367; Sasso et al., 1996, Expression of the immunoglobulin VH gene 51p1 is proportional to its germline gene copy number, Journal of Clinical Investigation 97(9):2074 2080) and exists in at least three haplotypes that carry duplications of the VHi-69 gene, which results in multiple copies of the VH gene at a given locus. These polymorphic alleles include differences in the complementarity determining regions (CDRs), which may dramatically influence antigen specificity. Table 2 sets for the reported alleles for human VH1 -69 and the SEQ ID NOs for the DNA and protein sequences of the mature heavy chain variable regions. Table 3 sets forth the reported alleles for human VH1-2 genes and the SEQ ID NOs for the DNA and protein sequences of the mature heavy chain variable regions. [000239] Representative genomic DNA and full-length protein sequences of a VH1-69 gene are set forth in SEQ ID NO: 1 and SEQ ID NO: 2, respectively. FIG. 13 and FIG. 14 set forth DNA and protein alignments of thirteen reported VH1-69 alleles, respectively. Representative 42 LUUlW1 NO. I o IA-VVU DNA and protein sequences of a VH1-2 gene are set forth in SEQ ID NO: 60 and SEQ ID NO: 61, respectively. FIG. 16 and FIG. 17 set forth DNA and protein alignments of five reported VH1-2 alleles, respectively. FIG. 15 and FIG. 18 set forth a percent identity/similarity matrix for aligned protein sequences corresponding to thirteen reported human VH1-69 alleles and five reported human VHi-2 alleges, respectively. In various embodiments, the modified locus of the invention comprises a VH gene selected from Table 1, present in two or more copy number, wherein the copy number includes up to and including the number of alleles shown in Table 1. In one embodiment, the modified locus of the invention comprises a VHi-69 gene selected from Table 2, present in two or more copy number, wherein the copy number includes up to and including the number of alleles shown in Table 1. In one embodiment, the modified locus of the invention comprises a VH1-2 gene selected from Table 3, present in two or more copy number, wherein the copy number includes up to and including the number of alleles shown in Table 1. [000240] Although embodiments employing a restricted human VH repertoire in a mouse are extensively discussed, other non-human animals that express a restricted human VH repertoire are also provided. Such non-human animals include any of those which can be genetically modified to express a restricted human VH repertoire as disclosed herein, including, e.g., mouse, rat, rabbit, pig, bovine (e.g., cow, bull, buffalo), deer, sheep, goat, chicken, cat, dog, ferret, primate (e.g., marmoset, rhesus monkey), etc. For example, for those non-human animals for which suitable genetically modifiable ES cells are not readily available, other methods are employed to make a non-human animal comprising the genetic modification. Such methods include, e.g., modifying a non-ES cell genome (e.g., a fibroblast or an induced pluripotent cell) and employing nuclear transfer to transfer the modified genome to a suitable cell, e.g., an oocyte, and gestating the modified cell (e.g., the modified oocyte) in a non-human animal under suitable conditions to form an embryo. Methods for modifying a non-human animal genome (e.g., a pig, cow, rodent, chicken, etc. genome) include, e.g., employing a zinc finger nuclease (ZFN) or a transcription activator-like effector nuclease (TALEN) to modify a genome to include a restricted human VH repertoire. Thus, in one embodiment a method is provided for editing a non-human animal genome to include a restricted human VH repertoire, comprising a step of editing the genome employing a ZFN or a TALEN to include no more than one, or no more than two, human VH gene segments (or polymorphic variants thereof), wherein the no more than one or no more than two human VH gene segments are operably linked to an immunoglobulin constant gene sequence. In one embodiment, the constant gene sequence is selected from a human heavy chain constant sequence and a non-human heavy chain constant sequence. In one embodiment, the constant sequence is non-human and the no more than one or no more than two human VH gene segments are operably linked to non-human constant gene sequence at an endogenous non-human immunoglobulin locus. 43 IJOCKe INO. 'IJIUA-VVU [000241] In one aspect, the non-human animal is a small mammal, e.g., of the superfamily Dipodoidea or Muroidea. In one embodiment, the genetically modified animal is a rodent. In one embodiment, the rodent is selected from a mouse, a rat, and a hamster. In one embodiment, the rodent is selected from the superfamily Muroidea. In one embodiment, the genetically modified animal is from a family selected from Calomyscidae (e.g., mouse-like hamsters), Cricetidae (e.g., hamster, New World rats and mice, voles), Muridae (true mice and rats, gerbils, spiny mice, crested rats), Nesomyidae (climbing mice, rock mice, with-tailed rats, Malagasy rats and mice), Platacanthomyidae (e.g., spiny dormice), and Spalacidae (e.g., mole rates, bamboo rats, and zokors). In a specific embodiment, the genetically modified rodent is selected from a true mouse or rat (family Muridae), a gerbil, a spiny mouse, and a crested rat. In one embodiment, the genetically modified mouse is from a member of the family Muridae, [000242] In one embodiment, the non-human animal is a rodent that is a mouse of a C57BL strain. In one embodiment, the C57BL strain is selected from C57BL/A, C57BL/An, C57BL/GrFa, C57BL/KaLwN, C57BL/6, C57BL/6J, C57BL/6ByJ, C57BL/6N, C57BL/6NJ, C57BL/10, C57BL/10ScSn, C57BL/10Cr, and C57BL/Ola. In another embodiment, the mouse is a 129 strain. In one embodiment, the 129 strain is selected from the group consisting of 129P1, 129P2, 129P3, 129X1, 129S1 (e.g., 129S1/SV, 129S1/SvIm), 129S2, 129S4, 129S5, 129S9/SvEvH, 129S6 (129/SvEvTac), 129S7, 129S8, 129T1, 129T2 (see, e.g., Festing et al. (1999) Revised nomenclature for strain 129 mice, Mammalian Genome 10:836, see also, Auerbach et a. (2000) Establishment and Chimera Analysis of 129/SvEv- and C57BL/6 Derived Mouse Embryonic Stem Cell Lines). In one embodiment, the genetically modified mouse is a mix of an aforementioned 129 strain and an aforementioned C57BL strain (e.g., a C57BL/6 strain). In another embodiment, the mouse is a mix of aforementioned 129 strains, or a mix of aforementioned C57BL/6 strains. In one embodiment, the 129 strain of the mix is a 129S6 (129/SvEvTac) strain. In another embodiment, the mouse is a mix of a 129/SvEv- and a C57BL/6-derived strain. In a specific embodiment, the mouse is a mix of a 129/SvEv- and a C57BL/6-derived strain as described in Auerbach et al. 2000 BioTechniques 29:1024-1032. In another embodiment, the mouse is a BALB strain, e.g., BALB/c strain. In another embodiment, the mouse is a mix of a BALB strain (e.g., BALB/c strain) and another aforementioned strain. [000243] In one embodiment, the non-human animal is a rat. In one embodiment, the rat is selected from a Wistar rat, an LEA strain, a Sprague Dawley strain, a Fischer strain, F344, F6, and Dark Agouti. In one embodiment, the rat strain is a mix of two or more of a strain selected from the group consisting of Wistar, LEA, Sprague Dawley, Fischer, F344, F6, and Dark Agouti. 44 LOUiKeT N4O. 'I OIU/A-VVU Table I VH Family VH Gene Alleles VH Family VH Gene Alleles 1-2 5 4-4 7 1-3 2 4-28 6 1-8 2 4-30-1 1 1-18 3 4-30-2 5 VH1 1-24 1 V4-30-4 6 1-45 3 4-31 10 1-46 3 4-34 13 1-58 2 4-39 7 1-69 13 4-59 10 4-61 8 2-5 10 VH2 2-26 1 VHS 5-51 5 2-70 13 VH6 6-1 2 3-7 3 3-9 2 VH7 7-4-1 5 3-11 4 7-81 1 3-13 4 3-15 8 3-16 2 3-20 1 3-21 4 3-23 5 3-30 19 3-30-3 2 3-30-5 1 VH3-33 6 3-35 1 3-38 2 3-43 2 3-48 4 3-49 5 3-53 4 3-64 5 3-66 4 3-72 2 3-73 2 3-74 3 45 IOCK9e imo. 'i/U/4-VVU Table 2 IgHV1-69 Allele Accession Number SEQ ID NO: (DNA/Protein) IgHV1-69*01 L22582 34/35 IgHV1-69*02 Z27506 36/37 IgHV1-69*03 X92340 38/39 IgHV1-69*04 M83132 40/41 IgHV1-69*05 X67905 42/43 IgHV1-69*06 L22583 44/45 IgHV1-69*07 Z29978 46/47 IgHV1-69*08 Z14309 48/49 IgHV1-69*09 Z14307 50/51 IgHV1-69*10 Z14300 52/53 IgHV1-69*11 Z14296 54/55 IgHV1-69*12 Z14301 56/57 IgHV1-69*13 Z14214 58/59 Table 3 IgHV1-2 Allele Accession Number SEQ ID NO: (DNA/Protein) IgHV1-2*01 X07448 60/61 IgHV1-2*02 X62106 62/63 IgHV1-2*03 X92208 64/65 IgHV1-2*04 Z12310 66/67 IgHV1-2*05 HM855674 68/69 Antigen-Dependent VH Gene Usage [000244] Antigen-dependent preferential usage Of VH genes can be exploited in the development of human therapeutics targeting clinically significant antigens. The ability to generate a repertoire of antibody variable domains using a particular VH gene can provide a significant advantage in the search for high-affinity antibody variable domains to use in human therapeutics. Studies on naive mouse and human VH gene usage in antibody variable domains reveal that most heavy chain variable domains are not derived from any particular single or dominantly used VH gene. On the other hand, studies of antibody response to certain antigens reveal that in some cases a particular antibody response displays a biased usage of a particular VH gene in the B cell repertoire following immunization. [000245] Although the human VH repertoire is quite diverse, by some estimates the expected frequency of usage of any given VH gene, assuming random selection of VH genes, is about 2% (Brezinschek et al., 1995, Analysis of the Heavy Chain Repertoire of Human Peripheral B Cells Using Single-Cell Polymerase Chain Reaction, J. Immunol. 155:190-202). But VH usage in peripheral B cells in humans is skewed. In one study, functional V gene abundance followed the pattern VH3 > VH4 > VH1 > VH2 > VHS > VH6 (Davidkova et al., 1997, Selective Usage of VH 46 UOCKet NO. W.IUA-VVU Genes in Adult Human Lymphocyte Repertoires, Scand. J. Immunol. 45:62-73). One early study estimated that VH3 family usage frequency was about 0.65, whereas VH1 family usage frequency was about 0.15; these and other observations suggest that the germline complexity of the human VH repertoire is not precisely reflected in the peripheral B cell compartment in humans that have a normal germline VH repertoire, a situation that is similar to that observed in the mouse-i.e., VH gene expression is non-stochastic (Zouali and These, 1991, Probing VH Gene-Family Utilization in Human Peripheral B Cells by In Situ Hybridization, J. Immunol. 146(8):2855-2864). According to one report, VH gene usage in humans, from greatest to least, is VH3 > VH4 > VH1 > VH5 > VH2 > VH6; rearrangements in peripheral B cells reveal that VH3 family usage is higher than to be expected based on the relative number of germline VH3 genes (Brezinschek et al., 1995). According to another report VH usage in humans follows the pattern VH3 > VH5 > VH2 > VH1 > VH4 > VH6, based on analysis of pokeweed mitogen-activated peripheral small immunocompetent B cells (Davidkova et al., 1997, Selective Usage of VH Genes in Adult Human B Lymphocyte Repertoires, Scand. J. Immunol. 45:62-73). One report asserts that among the most frequently used VH3 family members are 3-23, 3-30 and 3-54 (Brezinschek et al., 1995). In the VH4 family, member 4-59 and 4-4b were found relatively more frequently (1d.), as well as 4-39 and 4-34 (Brezinscheck et al., 1997, Analysis of the Human VH Gene Repertoire, J. Clin. Invest. 99(10):2488-2501). Others postulate that the activated heavy chain repertoire is skewed in favor of high VH5 expression and lower VH3 expression (Van Dijk Hard and Lundkvist, 2002, Long-term kinetics of adult human antibody repertoires, Immunology 107:136-144). Other studies assert that the most commonly used VH gene in the adult human repertoire is VH4-59, followed by VH3-23 and VH3-48 (Arnaout et al., 2001, High-Resolution Description of Antibody Heavy-Chain Repertoires in Humans, PLoS ONE 6(8):108). Although usage studies are based on relatively small sample numbers and thus exhibit high variance, taken together the studies suggest that V gene expression is not purely stochastic. Indeed, studies with particular antigens have established that-in certain cases-the deck is firmly stacked against certain usages and in favor of others. [000246] Over time, it became apparent that the observed repertoire of human heavy chain variable domains generated in response to certain antigens is highly restricted. Some antigens are associated almost exclusively with neutralizing antibodies having only certain particular VH genes, in the sense that effective neutralizing antibodies are derived from essentially only one VH gene. Such is the case for a number of clinically important human pathogens. [000247] VHi-69-derived heavy chains have been observed in a variety of antigen-specific antibody repertoires of therapeutic significance. For instance, VH1-69 was frequently observed in heavy chain transcripts of an IgE repertoire of peripheral blood lymphocytes in young children with atopic disease (Bando et a., 2004, Characterization of VHS gene expressed in PBL from children with atopic diseases: detection of homologous VH1-69 derived transcripts 47 IJL.'WL INU. I,) UMYVVJ from three unrelated patients, Immunology Letters 94:99-106). VH1-69-derived heavy chains with a high degree of somatic hypermutation also occur in B cell lymphomas (Perez et al., 2009, Primary cutaneous B-cell lymphoma is associated with somatically hypermutated immunoglobulin variable genes and frequent use of VH1-69 and VH4-59 segments, British Journal of Dermatology 162:611-618), whereas some VHi-69-derived heavy chains with essentially germline sequences (i.e., little to no somatic hypermutation) have been observed among autoantibodies in patients with blood disorders (Pos et al., 2008, VHI -69 germline encoded antibodies directed towards ADAMTS13 in patients with acquired thrombotic thrombocytopenic purpura, Journal of Thrombosis and Haemostasis 7:421-428). [000248] Further, neutralizing antibodies against viral antigens such as HIV, influenza and hepatitis C (HCV) have been found to utilize germline and/or somatically mutated VH1-69 derived sequences (Miklos et al., 2000, Salivary gland mucosa-associated lymphoid tissue lymphoma immunoglobulin VH genes show frequent use of VI-69 with distinctive CDR3 features, Blood 95(12):3878-3884; Kunert et a/., 2004, Characterization of molecular features, antigen-binding, and in vitro properties of IgG and IgM variants of 4E10, an anti-HIV type I neutralizing monoclonal antibody, Aids Research and Human Retroviruses 20(7):755-762; Chan et aL., 2001, VH1-69 gene is preferentially used by hepatitis C virus-associated B cell lymphomas and by normal B cells responding to the E2 viral antigen, Blood 97(4):1023-1026; Carbonari et al., 2005, Hepatitis C virus drives the unconstrained monoclonal expansion of VH1 69-expressing memory B cells in type il cryoglobulinemia: A model of infection-driven lymphomagenesis, Journal of Immunology 174:6532-6539; Wang and Palese, 2009, Universal epitopes of influenza virus hemagglutinins?, Nature Structural & Molecular Biology 16(3):233 234; Sui et al., 2009, Structural and functional bases for broad-spectrum neutralization of avian and human influenza A viruses, Nature Structural & Molecular Biology 16(3):265-273; Marasca et al., 2001, Immunoglobulin Gene Mutations and Frequent Use of VH1-69 and VH4-34 Segments in Hepatitis C Virus-Positive and Hepatitis C Virus-Negative Nodal Marginal Zone B Cell Lymphoma, Am. J. Pathol. 159(1):253-261). [000249] VH usage bias is also observed in the humoral immune response to Haemophilus influenzae type b (Hib PS) in humans. Studies suggest that the VHIll family (the VHII b subfamily in particular, VH9.1) exclusively characterizes the human humoral response to Hib PS, with diverse D and J genes (Adderson et a/., 1991, Restricted Ig H Chain V Gene Usage in the Human Antibody Response to Haemophilus influenzae Type b Capsular Polysaccharide, J. Immunol. 147(5):1667-1674; Adderson et al, 1993, Restricted Immunoglobulin VH Usage and VDJ Combinations in the Human Response to Haemophilus influenzae Type b Capsular Polysaccharide, J. Clin. Invest. 91:2734-2743). Human JH genes also display biased usage; JH and JH 6 are observed at about 38-41% in peripheral B cells in humans (Brezinschek et al., 1995). 48 LJOCKel OT . '1 U/A-VVU [000250] VH usage in HIV-1 -infected humans is reportedly biased against VH3 usage and in favor of VH1 and VH4 gene families (Wisnewski et aL, 1996, Human Antibody Variable Region Gene Usage in HIV-1 Infection, J. Acquired Immune Deficiency Syndromes & Human Retroviology 11(1):31-38). However, cDNA analysis of bone marrow from affected patients' revealed significant VH 3 usage not expressed in the functional B cell repertoire, where Fabs reflecting the VH3 usage exhibited effective in vitro neutralization of HIV-1 (/d.). It might be postulated that the humoral immune response to HIV-1 infection is possibly attenuated due to the VH restriction; modified non-human animals as described herein (not infectable by HIV-1) might thus be useful for generating neutralizing antibody domains derived from particular VH genes present in the genetically modified animals described herein, but derived from different VH genes than those observed in the restricted repertoire of affected humans. [000251] Thus, the ability to generate high affinity human antibody variable domains in VH restricted mice, e.g., (restricted, e.g., to a VH3 family member and polymorph(s) thereof) immunized with HIV-1 might provide a rich resource for designing effective HIV-1 -neutralizing human therapeutics by thoroughly mining the restricted (e.g., restricted to a VH3 family member or variant(s) thereof) repertoire of such an immunized mouse. [000252] Restriction of the human antibody response to certain pathogens may reduce the likelihood of obtaining antibody variable regions from affected humans that can serve as springboards for designing high affinity neutralizing antibodies against the pathogen. For example, the human immune response to HIV-1 infection is clonally restricted throughout HIV-1 infection and into AIDS progression (Muller et al., 1993, B-cell abnormalities in AIDS: stable and clonally restricted antibody response in HIV-1 infection, Scand. J. Immunol. 38:327-334; Wisnewski et al., 1996). Further, VH genes are in general not present in all polymorphic forms in any particular individual; certain individuals in certain populations possess one variant, whereas individuals in other populations possess a different variant. Thus, the availability of a biological system that is restricted to a single VH gene and its variants will in various embodiments provide a hitherto unexploited source of diversity for generating antibody variable regions (e.g., human heavy and light cognate domains) based on a restricted VH gene. Thus, in one aspect, a genetically modified non-human animal is provided that comprises a plurality of polymorphic variants of no more than one, or no more than two, human VH gene segment family member. In one embodiment, the no more than one, or no more than two, human VH gene segments are operably linked to one or more human DH gene segments, one or more human JH gene segments, and a human or non-human constant region gene segment. In one embodiment the constant region is at an endogenous non-human immunoglobulin constant gene locus. In one embodiment, the non-human animal further comprises a nucleic acid sequence derived from a human VL sequence, e.g., a rearranged or unrearranged human VL gene segment or a rearranged human VL/JL sequence. In one embodiment, the nucleic acid 49 IJOCKei PiO. 'IJIUA-VVVJ sequence derived from the human VL sequence is at an endogenous non-human VL gene locus; in one embodiment, the nucleic acid sequence derived form the human VL sequence is on a transgene. In a specific embodiment, the non-human animal is incapable of expressing an immunoglobulin light chain variable domain that itself comprises an endogenous VL or JL gene segment, and comprises no more than one, or no more than two, light chain genes that encode rearranged human VL domains (i.e., from no more than one, or no more than two, rearranged human VL/JL sequences). [000253] Genetically modified mice that express human heavy chain variable regions with restricted VH gene segment usage are useful to generate a relatively large repertoire of junctionally diverse, combinatorially diverse, and somatically mutated high affinity human immunoglobulin heavy chain variable regions from an otherwise restricted repertoire. A restricted repertoire, in one embodiment, refers to a predetermined limitation in the number and/or identity of germline genes that results in the mouse being unable to form a rearranged heavy chain gene that is derived from any V gene other than a preselected V gene. In embodiments that employ a preselected V gene but not a preselected D and/or J gene, the repertoire is restricted with respect to the identity of the V gene but not the D and/or J gene (e.g., the repertoire consists essentially of no more than one, or no more than two, VH gene segments (and/or polymorphs thereof); and a plurality of D gene segments and a plurality of J gene segments)). The identity of the preselected V gene (and any preselected D and/or J genes) is not limited to any particular V gene. [000254] Designing a mouse so that it rearranges a single VH gene (present as a single segment or a set of variants) with a variety of human D and J gene segments (e-g., DH and JH segments) provides an in vivo junctional diversity/combinatorial diversity/somatic hypermutation permutation machine that can be used to iterate mutations in resulting rearranged heavy chain variable region sequences (e.g., V/D/J or V/J, as the case may be). In such a mouse, the clonal selection process operates to select suitable variable regions that bind an antigen of interest that are based on a single preselected VH gene (or variants thereof). Because the mouse's clonal selection components are dedicated to selection based on the single preselected VH gene segment, background noise (e.g., a wide variety of non antigen-binding VH domains derived from many germline gene segments) is largely eradicated. With judicious selection of the VH gene segment, a relatively larger number of clonally selected, antigen specific antibodies can be screened in a shorter period of time than with a mouse with a large diversity of V segments. [000255] Preselecting limited repertoire and restricting a mouse to a single V segment provides a system for permuting V/D/J junctions at a rate that is in various embodiments higher than that observed in mice that otherwise have up to 40 or more V segments to recombine with D and J regions. Removal of other V segments frees the locus to form more V/D/J 50 LJOCKeX 140. 'I5/VA-VVU combinations for the preselected V segment than otherwise observed. The increased number of transcripts that result from the recombination of the preselected V with one of a plurality of D and one of a plurality of J segments will feed those transcripts into the clonal selection system in the form of pre-B cells, and the clonal selection system is thus dedicated to cycling B cells that express the preselected V region. In this way, more unique V region rearrangements derived from the preselected V segment can be screened by the organism than would otherwise be possible in a given amount of time. [000256] In various aspects, mice are described that enhance the junctional diversity of V/D/J recombinations for the preselected V region, because all or substantially all recombinations of the immunoglobulin heavy chain variable locus will be of the preselected V segment and the D and J segments that are placed in such mice. Therefore, the mice provide a method for generating a diversity of CDR3 segments using a base, or restricted VH gene repertoire. [000257] In one aspect, a non-human animal is provided, wherein the B cell population of the non-human animal expresses immunoglobulin heavy chains that are derived from no more than one, or no more than two human VH gene segments. In one embodiment, each of the no more than one, or no more than two, human VH gene segments are present in two or more polymorphic forms. In one embodiment, the human VH gene segment is present in three, four, five, six, seven, eight, nine, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 or 20 polymorphic forms. In one embodiment, the non-human animal expresses a human light chain variable domain derived from a human VL gene segment. [000258] In one aspect, a method is provided for generating a B cell population in a non human animal, wherein the B cell population expresses human heavy chains derived from a single germline human VH gene segment and two or more human D gene segments and two or more human J gene segments; the method comprising a step of immunizing a non-human animal as described herein with an antigen of interest, and allowing the non-human animal to mount an immune response to the antigen of interest, wherein the immune response comprises expressing the human heavy chains on the surface of B cells in the B cell population In one embodiment, the non-human animal is a rodent (e.g., a mouse or rat). In one embodiment, the human VH gene segment, human DH segment, and human JH segment are operably linked to a non-human constant region gene. In one embodiment, the non-human animal further comprises a nucleic acid sequence encoding a human VL domain. In one embodiment, the nucleic acid sequence encoding the human VL domain is linked to a non-human light chain constant region gene sequence. [000259] In one aspect, a method for making a non-human animal that expresses an immunoglobulin population characterized by the immunoglobulins having heavy chains that are derived from a plurality of rearrangements of a single human VH gene segment (or sing human VH gene family member) and one of a plurality of DH gene segments and one of a plurality Of JH 51 UOCKeT NO. '5fUA-VVU gene segments, is provided. In one embodiment, the human VH gene segment is a human VH1-69 gene segment. In one embodiment, the human VH gene segment is a human VH1-2 gene segment. [000260] In one aspect, a method is provided for generating a population of human immunoglobulin heavy chain variable domains whose CDR1 and CDR2 are derived from the same germline VH gene segment, and whose CDR3 are derived from the germline gene segment and two or more human D segments, and two or more human J segments; the method comprising immunizing a non-human animal as described herein with an antigen of interest, and allowing the non-human animal to mount an immune response to the antigen of interest, wherein the immune response comprises expressing the human heavy chain variable domains in the context of a light chain variable domain. In one embodiment, the non-human animal is a rodent (e.g., a mouse or rat). In one embodiment, the human VH gene segment, human D segment, and human J segment are operably linked to a non-human constant region gene. In one embodiment, the non-human animal further comprises a nucleic acid sequence encoding a human VL domain. In one embodiment, the nucleic acid sequence encoding the human VL domain is linked to a non-human light chain constant region gene sequence. [000261] In one aspect, a genetically modified non-human animal is provided, wherein the non-human animal is incapable of expressing a non-human VH domain, and wherein each immunoglobulin heavy chain of the heavy chain population expressed in the animal comprises a human VH domain comprising a CDR1 and a CDR2 that are identical but for one or more somatic hypermutations, and wherein the heavy chain population comprises a plurality of CDR3 sequences derived from a plurality of rearrangements with a plurality of D and J gene segments. [000262] In one aspect, a biological system for generating variation in CDR3 identity and length is provided, comprising a genetically modified non-human animal as described herein, wherein the non-human animal comprises no more than or no more than two human VH gene segments, and two or more D gene segments and one or more J gene segments, wherein the non-human animal further comprises a humanized immunoglobulin light chain locus. In various embodiments, the non-human animal in response to immunization with an antigen of interest generates an immune response that comprises expressing an immunoglobulin heavy chain population characterized by each heavy chain having CDR1s and CDR2s that differ only by somatic hypermutation, and CDR3s that differ by rearrangement and somatic hypermutation. In one embodiment, the biological system is a mouse that is genetically modified as described herein. In one embodiment, the human VH gene segment and the human VL gene segment are at endogenous mouse heavy and light immunoglobulin loci, respectively. In one embodiment, one or more of the human VH gene segment and the human VL gene segment are on transgenes (i.e., at a locus other than an endogenous immunoglobulin locus). 52 L/UUWL INU. IOIU/-VVJ EXAMPLES [000263] The following examples are provided so as to describe to those of ordinary skill in the art how to make and use methods and compositions of the invention, and are not intended to limit the scope of what the inventors regard as their invention. Unless indicated otherwise, temperature is indicated in Celsius, and pressure is at or near atmospheric. In the foregoing Examples, when the use of kits and/reagents from various suppliers is indicated, all procedures were carried out according to manufacturer's specifications. Example I Construction of Restricted Heavy Chain Loci [000264] A uniquely engineered human heavy chain locus containing a single human VH gene segment located upstream of all the human DH and JH gene segments was created by a series of homologous recombination reactions in bacterial cells (BHR) using Bacterial Artificial Chromosome (BAC) DNA. Several targeting constructs for creation of a single VH containing heavy chain locus were constructed using VELOCIGENE@ genetic engineering technology (see, e.g., US Pat. No. 6,586,251 and Valenzuela, D.M. et al. (2003) High-throughput engineering of the mouse genome coupled with high-resolution expression analysis. Nature Biotechnology 21(6): 652-659). [000265] Construction of a Human VH1-69 Restricted Heavy Chain Locus. Briefly, four modifications were performed using human BAC DNA to create a targeting construct containing a human VH1-69 gene segment with all the human DH and JH segments (FIG. 1). In the first modification, a modified human BAC containing multiple distal (5') human VH gene segments, including VH1-69, an upstream hygromycin selection cassette and a 5' mouse homology arm was targeted with a second spectinomycin cassette, which also contained a modified recombination signal sequence (RSS; BHR 1, FIG. 1, top left). This modified recombination signal sequence (RSS) introduced two point mutations (T to A and G to A) in the 3' RSS region of the human VH1-69 gene changing the RSS nonamer to the optimal consensus sequence. Thus, the first modification (BHR 1) created a human genomic fragment containing the human VH1-69 gene segment with a modified 3' RSS, a unique AsiSI restriction site about 180 bp downstream of the RSS and a spectinomycin cassette (FIG. 1, middle left). [000266] The second modification (BHR 2) included the use of a neomycin (Neo) cassette flanked by Frt sites to delete the hygromycin cassette and 5' human VH gene segments upstream of the VH1-69 gene segment. This modification was targeted 5' to the human VH1-69 gene segment to leave intact about 8.2 kb of the promoter region of human VH1-69 and the 5' mouse homology arm (FIG. 1, bottom left). [000267] The third modification (BHR 3) included another spectinomycin cassette flanked by uniquely engineered 5' PI-Scel and 3' AsiSI sites targeted to a human genomic fragment 53 LJOCKez No'1. I 1UA-VVU containing the first three functional human VH gene segments and all the human DH and JH gene segments (FIG. 1, middle right). The human genomic fragment was previously targeted with a neomycin cassette and contained 5' and 3' homology arms containing the mouse genomic sequence 5' and 3' of the endogenous heavy chain locus including the 3' intronic enhancer and the IgM gene. This modification deleted the 5' mouse genomic sequence and human VH gene segments, leaving about 3.3 kb of the VH-DH intergenic region upstream of the human DH1-1 gene segment, all of the human DH and JH segments, and the 3' mouse genomic fragment containing the 3' intronic enhancer and the IgM gene (FIG. 1, bottom right). [000268] The fourth modification was achieved by employing the unique PI-Scel and AsiSI sites (described above) to ligate the two modified BACs from BHR 2 and BHR 3 (FIG. 1, bottom center), which yielded the final targeting construct. The final targeting construct for the creation of a modified heavy chain locus containing a single human VH gene segment and all the human DH and JH gene segments in ES cells contained, from 5' to 3', a 5' homology arm containing about 20 kb of mouse genomic sequence upstream of the endogenous heavy chain locus, a 5' Frt site, a neomycin cassette, a 3' Frt site, about 8.2 kb of the human VH1-69 promoter, the human VH1- 6 9 gene segment with a modified 3' RSS, 27 human DH gene segments, six human JH segments, and a 3' homology arm containing about 8 kb of mouse genomic sequence downstream of the mouse JH gene segments including the 3' intronic enhancer and IgM gene (FIG. 1, bottom). The Human VH1 -69 Targeting Vector (SEQ ID NO: 3) was linearized and electroporated into mouse ES cells heterozygous for a deletion of the endogenous heavy chain locus. [000269] Construction of a Human VHI-2 Restricted Heavy Chain Locus. Using the steps described above, other polymorphic VH gene segments in the context of mouse heavy chain constant regions are employed to construct a series of mice having a restricted number immunoglobulin heavy chain V segments (e.g., 1, 2, 3, 4, or 5), wherein the V segments are polymorphic variants of a V gene family member. Exemplary polymorphic VH gene segments are derived from human VH gene segments including, e.g., VH1-2, VH2-26, VH2-70 and VH3-23. Such human VH gene segments are obtained, e.g., by de novo synthesis (e.g., Blue Heron Biotechnology, Bothell, WA) using sequences available on published databases. Thus, DNA fragments encoding each VH gene are, in some embodiments, generated independently for incorporation into targeting vectors, as described herein. In this way, multiple modified immunoglobulin heavy chain loci comprising a restricted number of VH gene segments are engineered in the context of mouse heavy chain constant regions. An exemplary targeting strategy for creating a restricted humanized heavy chain locus containing a human VHI-2 gene segment, 27 human DH gene segments, and six human JH gene segments is shown in FIG. 2. [000270] Briefly, a modified human BAC clone containing three human VH gene segments (VH6-1, VH1-2, VHl-3), 27 human DH gene segments, and six human JH gene segments (see 54 U GIWKL 1IU. iIOU-VVU USSN 13/404,075; filed 24 February 2012, herein incorporated by reference) is used to create a restricted humanized heavy chain locus containing a human VH1-2 gene segment. This modified BAC clone functionally links the aforementioned human heavy chain gene segments with the mouse intronic enhancer and the IgM constant region. The restricted human VH1-2 based heavy chain locus is achieved by two homologous recombinations using the modified human BAC clone described above. [000271] For the first homologous recombination, 205 bp of the human VH6-1 gene segment (from about 10 bp upstream (5') of the VH6-1 start codon in exon 1 to about 63 bp downstream (3') of the beginning of exon 2) in the modified human BAC clone is deleted by bacterial homologous recombination using a spectinomycin (aadA) cassette flanked by unique PI-Scel restriction sites (FIG. 2, BHR 1). This allows for subsequent removal of the aadA cassette without disrupting other human gene segments within the restricted heavy chain locus. [000272] For the second homologous recombination, the 5' end of the modified human BAC clone including the entire human VH1- 3 gene segment and about 60 bp downstream (3') of the gene segment is deleted by homologous recombination using a hygromycin cassette containing flanking 5' AsiSI and 3' Ascl restriction sites (FIG. 2, BHR 2). As described above, the spectinomycin cassette is optionally removed after confirmation of the final targeting vector including deletion of the two human VH gene segments flanking the human VHl-2 gene segment (FIG. 2, bottom). An exemplary human VH1-2 targeting vector is set forth in SEQ ID NO: 70. [000273] Employing polymorphic VH gene segments in a restricted immunoglobulin heavy chain locus represents a novel approach for generating antibodies, populations of antibodies, and populations of B cells that express antibodies having heavy chains with diverse CDRs derived from a single human VH gene segment. Exploiting the somatic hypermutation machinery of the host animal along with combinatorial association with rearranged human immunoglobulin light chain variable domains results in the engineering of unique heavy chains and unique VHNL pairs that expand the immune repertoire of genetically modified animals and enhance their usefulness as a next generation platform for making human therapeutics, especially useful as a platform for making neutralizing antibodies specific for human pathogens. [000274] Thus, using the strategy outlined above for incorporation of additional and/or other polymorphic VH gene segments into the mouse immunoglobulin heavy chain locus allows for the generation of novel antibody repertoires for use in neutralizing human pathogens that might otherwise effectively evade the host immune system. [000275] Targeted ES cells described above were used as donor ES cells and introduced into an 8-cell stage mouse embryo by the VELOCIMOUSE@ method (supra). Mice bearing a humanized heavy chain locus containing a single human VH gene segment, all the human DH and JH gene segments operably linked to the mouse immunoglobulin constant region genes 55 LJOCKO iO. 'l JUA-VVVj were identified by genotyping using a modification of allele assay (Valenzuela et al., supra) that detected the presence of the neomycin cassette, the human VH gene segment and a region within the human DH and JH gene segments as well as endogenous heavy chain sequences. Table 4 sets forth the primers and probes used in this assay to confirm mice harboring a restricted heavy chain locus containing a single human VH1-69 gene segment, 27 human DH gene segments and six human JH gene segments. [000276] Mice bearing an engineered heavy chain locus that contains a single human VH gene segment can be bred to a FLPe deletor mouse strain (see, e.g., Rodriguez, C.I. et al. (2000) High-efficiency deleter mice show that FLPe is an alternative to Cre-/oxP. Nature Genetics 25: 139-140) in order to remove any Frt'ed neomycin cassette introduced by the targeting vector that is not removed, e.g., at the ES cell stage or in the embryo. Optionally, the neomycin cassette is retained in the mice. [000277] Pups are genotyped and a pup heterozygous for a humanized heavy chain locus containing a single human VH gene segment, all the human DH and JH segments operably linked to the endogenous mouse immunoglobulin constant genes is selected for characterizing the immunoglobulin heavy chain repertoire. Table 4 Name Sequence (5'-3') SEQ ID (Region Detected) NO: hyg Forward: TGCGGCCGAT CTTAGCC 4 (hygromycin Reverse: TTGACCGATT CCTTGCGG 5 cassette) Probe: ACGAGCGGGT TCGGCCCATT C 6 neo Forward: GGTGGAGAGG CTATTCGGC 7 (neomycin Reverse: GAACACGGCG GCATCAG 8 cassette) Probe: TGGGCACAAC AGACAATCGG CTG 9 hgH9T Forward: TCCTCCAACG ACAGGTCCC 10 (human DH - H Reverse: GATGAACTGA CGGGCACAGG 11 genomic Probe: TCCCTGGAAC TCTGCCCCGA CACA 12 sequence) 77h3 Forward: CTCTGTGGAA AATGGTATGG AGATT 13 (human VH1 -69 Reverse: GGTAAGCATA GAAGGTGGGT ATCTTT 14 gene segment) Probe: ATAGAACTGT CATTTGGTCC AGCAATCCCA 15 mlgHA7 Forward: TGGTCACCTC CAGGAGCCTC 16 (mouse DH - JH Reverse: GCTGCAGGGT GTATCAGGTG C 17 genomic Probe: AGTCTCTGCT TCCCCCTTGT GGCTATGAGC 18 sequence) 88710T Forward: GATGGGAAGA GACTGGTAAC ATTTGTAC 19 (mouse 3' VH Reverse: TTCCTCTATT TCACTCTTTG AGGCTC 20 genomic Probe: CCTCCACTGT GTTAATGGCT GCCACAA 21 sequence) 56 LJOCKT NO. l4fUA-VVU migHd1O Forward: GGTGTGCGAT GTACCCTCTG AAC 22 (mouse 5' VH Reverse: TGTGGCAGTT TAATCCAGCT TTATC 23 genomic Probe: CTAAAAATGC TACACCTGGG GCAAAACACC 24 sequence) TG mIgHp2 Forward: GCCATGCAAG GCCAAGC 25 (mouse J Reverse: AGTTCTTGAG CCTTAGGGTG CTAG 26 equene) Probe: CCAGGAAAAT GCTGCCAGAG CCTG 27 Example 2 Characterization of Mice Expressing Heavy Chains Derived From a Single Human VH Gene Segment [000278] Mice homozygous for a single human VH gene segment at the endogenous heavy chain locus as described in Example 1 were evaluated for expression and B cell development using flow cytometry. [000279] Briefly, spleens and bone marrow was harvested from wild type (n=3 per group; six weeks old, male and female) and mice homozygous for a single human VH gene segment, all human DH and JH gene segments operably linked to mouse heavy chain constant regions. Red blood cells from spleens were lysed with ACK lysis buffer (Lonza Walkersville), followed by washing with complete RPMI medium. [000280] Flow cytometry. Cells (1x106) were incubated with anti-mouse CD16/CD32 (2.4G2, BD PHARMINGEN") on ice for 10 minutes, followed by labeling with the following antibody panels for 30 minutes on ice. Bone marrow panel: anti-mouse FITC-CD43 (1 B1 1, BioLegend), PE-ckit (2B8, BIOLEGEND@), PeCy7-IgM (11/41, EBIOSCIENCE@), PerCP-Cy5.5 IgD (11-26c.2a, BIOLEGEND@), APC-eFluor 780-B220 (RA3-6B2, EBIOSCIENCE@), APC CD19 (MB19-1, EBIOSCIENCE@). Bone marrow and spleen panel: anti-mouse FITC-IgK (187.1, BD Biosciences), PE-Ig2. (RML-42, BIOLEGEND@), PeCy7-IgM (11/41, EBIOSCIENCE®), PerCP-Cy5.5-]gD (11-26c.2a, BIOLEGEND®), Pacific Blue-CD3 (17A2, BIOLEGEND®), APC-B220 (RA3-6B2, EBIOSCIENCE@), APC-H7-CD19 (ID3, BD Biosciences). Bone marrow: immature B cells (B220intlgM*), mature B cells (B220h'IgM*), pro B cells (CD19*ckit*CD43*), pre B cells (CD19*ckit-CD43~), immature IgK B cells (B220'ilgM~lgK+lgk~), immature Igk* B cells (B220intlgM+lg-lgX+), mature IgK* B cells (B220hlgM+lgK+lgK~), mature lgk* B cells (B220QilgM+lgKIg*). Spleen: B cells (CD19*), mature B cells (CD19'IgDhilgMint), transitional/immature B cells (CD19*IgDintlgMhi). Bone marrow and spleen: IgK* B cells (CD19*1gK+lg-), lgk* B cells (CD191gK-Igk*). [000281] Following staining, cells were washed and fixed in 2% formaldehyde. Data acquisition was performed on a LSRII flow cytometer and analyzed with FLOWJO TM software (Tree Star, Inc.). Results for the splenic compartment are shown in FIGs. 3, 4A and 5 - 7. Results for the bone marrow compartment are shown in FIGs. 4B and 8 - 11 B. 57 L/UIWL IMU. I,')[ UK-Vv J [000282] Human VH Expression. Expression of the human VH1-69 gene segment was determined for mice heterozygous and homozygous for a human VH1-69 gene segment, all human DH and JH gene segments operably linked to mouse heavy chain constant regions by a quantitative PCR assay using TAQMAN* probes. [000283] Briefly, CD19* B cells were purified from the spleens of groups of mice (n=3 per group) using mouse CD19 microbeads (Miltenyi Biotec) according to manufacturer's specifications. Total RNA was purified using the RNEASY TM Mini kit (Qiagen) and genomic RNA was removed using an RNase-free DNase on-column treatment (Qiagen). About 200 ng mRNA was reverse-transcribed into cDNA using the First Stand cDNA Synthesis kit (Invitrogen), followed by amplification with the TAQMAN@ Universal PCR Master Mix (Applied Biosystems) using the ABI 7900 Sequence Detection System (Applied Biosystems). Unique primer/probe combinations were employed to specifically determine expression of human VH1 69-derived heavy chains (Table 5). Relative expression was normalized to the mouse X constant region (mCK). The results are shown in FIG. 12. Table 5 Name Sequence (5'-3') SEQ ID NO: Sense: AACTACGCAC AGAAGTTCCA GG 28 higHVI-69 Anti-sense: GCTCGTGGAT TTGTCCGC 29 Probe: CAGAGTCACG ATTACC 30 Sense: TGAGCAGCAC CCTCACGTT 31 mCK Antisense: GTGGCCTCAC AGGTATAGCT GTT 32 Probe: ACCAAGGACG AGTATGAA 33 Example 3 Humoral Immune Response in Mice Expressing Heavy Chains Derived From a Single Human VH Gene Segment [000284] The humoral immune response was determined for mice homozygous for human heavy and x light chain variable gene loci (HK) and mice homozygous for a single human VH gene segment, all human DH and JH gene segments operably linked to mouse heavy chain constant regions (1hVH HO) by comparative immunization using a human cell surface receptor (Antigen A). [000285] Immunization. Serum was collected from groups of mice prior to immunization with the above antigen. Antigen (2.35 pg each) was administered in an initial priming immunization mixed with 10 pg of CpG oligonucleotide (Invivogen) and 25 pg of Adju-phos (Brenntag) as adjuvants. The immunogen was administered via footpad (f.p.) in a volume of 25 pl per mouse. Subsequently, mice were boosted via f.p. with 2.3 pg of antigen along with 10 pg CpG and 25 pg Adju-Phos as adjuvants on days 3, 6, 11, 13, 17, and 20 for a total of six boosts. Mice were 58 UoCKeT NO. 14 UA-VVU bled on days 15 and 22 after the fourth and sixth boosts, respectively, and antisera were assayed for antibody titers to Antigen A. [000286] Antibody titers were determined in sera of immunized mice using an ELISA assay. Ninety six-well microtiter plates (Thermo Scientific) were coated with Antigen A (1 pg/ml) in phosphate-buffered saline (PBS, Irvine Scientific) overnight at 40C. The following day, plates were washed with phosphate-buffered saline containing 0.05% Tween 20 (PBS-T, Sigma Aldrich) four times using a plate washer (Molecular Devices). Plates were then blocked with 250 pt of 1% bovine serum albumin (BSA, Sigma-Aldrich) in PBS and incubated for one hour at room temperature. The plates were then washed four times with PBS-T. Sera from immunized mice and pre-immune sera were serially diluted ten-fold in 0.1% BSA PBS-T starting at 1:100 and added to the blocked plates in duplicate and incubated for one hour at room temperature. The last two wells were left blank to be used as secondary antibody control. The plates were again washed four times with PBS-T in a plate washer. A 1:5000 dilution of goat anti-mouse IgG-Fc-Horse Radish Peroxidase (HRP, Jackson Immunoresearch) conjugated secondary antibody was added to the plates and incubated for one hour at room temperature. Plates were again washed eight times with PBS-T and developed using TMB/H 2 0 2 as substrate. The substrate was incubated for twenty minutes and the reaction stopped with 1 N H 2

SO

4 (VWR). Plates were read on a spectrophotometer (Victor, Perkin Elmer) at 450 nm. Antibody titers were calculated using GRAPHPAD PRISMTM (GraphPad Software, Inc). [000287] Serum titer was calculated as serum dilution within experimental titration range at the signal of antigen binding equivalent to two times above background. Antibody titer for the humoral immune response against a human cell surface receptor (Antigen A) is set forth in FIG. 19. [000288] In a similar experiment, humoral immune responses were determined for mice homozygous for human heavy and x light chain variable gene loci (HK) and mice homozygous for a single human VH gene segment, all human DH and JH gene segments operably linked to mouse heavy chain constant regions (1hVH HO) by comparative immunization using influenza viral vaccines FLUVIRIN@ (Novartis Vaccines) and FLUMIST@ (MedImmune LLC). [000289] Briefly, serum was collected from groups of mice prior to immunization with the above antigen (as described above). Mice (n=5) homozygous for a single human VH gene segment (VH1-69), all human DH and JH gene segments operably linked to mouse heavy chain constant regions (1 hVH HO) were immunized intra-nasally (i.n.) with FLUMIST@ (live attenuated influenza vaccine) at 1/3 the normal dose/mouse. One normal dose of FLUMIST@ contains 106-5-7-5 FFU (fluorescent focus units) of live attenuated influenza vaccine. Therefore, each mouse was primed with 70 pl FLUMIST@ on day 1 followed by i.n. boost on days 3, 6, 11, 13, 17, 20 for a total of 6 boosts. No adjuvants were employed in this immunization. The mice 59 IJUUIWL IVAU. IOI>fV/VVUJ were bled on days 15 and 22 after 4th and 6th boosts respectively and antiserum assayed for antibody titers to FLUMIST@ (as described above). [000290] In a similar manner, in immunizations with FLUVIRIN@, pre-immune serum was collected from mice prior to initiation of immunization. Mice (n=5) homozygous for a single human VH gene segment (VH1-69), all human DH and JH gene segments operably linked to mouse heavy chain constant regions (1 hVH HO) were immunized with FLUVIRIN@ (trivalent inactivated influenza vaccine) via footpad (f p.) with 0.75 pg each of hemagglutinin/mouse/boost. Mice were primed on day 1 followed by f.p. boost on days 3, 6, 11, 13, 17, 20 for a total of 6 boosts. No adjuvants were employed in this immunization. The mice were bled on days 15 and 22 after 4th and 6th boosts respectively and antiserum assayed for antibody titers to FLUVIRIN@ (as described above). [000291] Serum titer was calculated as serum dilution within experimental titration range at the signal of antigen binding equivalent to two times above background. Antibody titer for the humoral immune response against FLUMIST® and FLUVIRIN@ is set forth in FIG. 20. [000292] As shown in this Example, antibody titers generated in 1 hVH HO mice were comparable to those generated in mice having a plurality of human VH gene segments (HK) for both a human cell surface receptor and a viral antigen (e.g., influenza). Thus, mice having immunoglobulin heavy chain loci restricted to a single VH gene segment are capable of mounting a robust immune response to antigen in a manner comparable to mice having immunoglobulin heavy chain loci containing a plurality of human VH gene segments (e.g., 80 VH). Example 4 Analysis of Antibody Gene Usage and CDR3 Length in Mice Having a Restricted Immunoglobulin Heavy Chain Locus [000293] Splenocytes harvested from mice homozygous for a single human VH gene segment at the endogenous heavy chain locus and homozygous for a replacement of the endogenous K light chain variable loci with human K light chain variable loci immunized with a human cell surface receptor (Antigen A) were analyzed for heavy and light chain gene segment usage by reverse-transcriptase polymerase chain reaction (RT-PCR) on mRNA from splenic B cells. [000294] Briefly, spleens were harvested and homogenized in IxPBS (Gibco) using glass slides. Cells were pelleted in a centrifuge (500xg for 5 minutes), and red blood cells were lysed in ACK Lysis buffer (Gibco) for 3 minutes. Cells were washed with 1xPBS and filtered using a 0.7pm cell strainer. B-cells were isolated from spleen cells using MACS magnetic positive selection for CD19 (Miltenyi Biotec). Total RNA was isolated from pelleted B-cells using the RNeasy Plus Kit (Qiagen). PolyA* mRNA was isolated from total RNA using the Oligotex® Direct mRNA mini kit (Qiagen). 60 LJUqKWL 0NU. IVIUA-VVNJ [000295] Double-stranded cDNA was prepared from splenic B cell mRNA by 5' RACE using the SMARTerTM Pico cDNA Synthesis Kit (Clontech) with substitution of the supplied reverse transcriptase and dNTPs with Superscript® @| and dNTPs (Invitrogen). VH and Vw antibody repertoires were amplified from the cDNA using primers specific for IgM, IgG, or IgK constant regions and the SMARTer T M 5' RACE primer (Table 6). PCR products were purified using a QlAquick@ PCR Purification Kit (Qiagen). A second round of PCR was done using the same 5' RACE primer and a nested 3' primer specific for the IgM, IgG, or Igi constant regions (Table 7). Second round PCR products were purified using a SizeSelect T M E-Gel@ system (Invitrogen). A third PCR was performed with primers that added 454 adapters and barcodes. Third round PCR products were purified using Agencourt® AMPure® XP Beads (Beckman Coulter). Purified PCR products were quantified by SYBR@ qPCR using a KAPA Library Quantification Kit (KAPA Biosystems). Pooled libraries were subjected to emulsion PCR (emPCR) using a 454 GS Junior Titanium Series Lib-A emPCR Kit (Roche Diagnostics) and bidirectional sequencing using Roche 454 GS Junior instrument according to manufacturer's specifications. [000296] Bioinformatic analysis. The 454 sequences were sorted based on the sample barcode perfect match and trimmed for quality. Sequences were annotated based on alignment of rearranged immunoglobulin sequences to human germline V(D)J segment database using local installation of Igblast (NCBI, v2.2.25+). A sequence was marked as ambiguous and removed from analysis when multiple best hits with identical score were detected. A set of perl scripts was developed to analyze results and store data in mysql database. CDR3 region was defined between conserved C codon and FGXG motif for light and WGXG motif for heavy chains. CDR3 length was determined using only productive antibodies. From the nucleic acid sequences and predicted amino acid sequences of the antibodies, gene usage was identified for IgM-primed (15,650), IgG-primed (18,967), and IgK primed (26,804) sequences. Results are shown in Table 8, Table 9, FIG. 21 and FIG. 22. [000297] Table 8 sets forth the percentage of observed human DH and JH gene segments used among IgM-primed (15,650 sequences) and IgG-primed (18,967 sequences) VH1-69 derived heavy chain variable region sequences. Human DH4-4/DH4-11 and human DH5-5/DH5 18 gene segments are presented in Table 8 together due to identical sequence identity between the respective pairs of DH gene segments. Table 9 sets forth the percentage of human VK and JK gene segments observed among light chains (26,804 sequences) cognate with VH1-69 derived heavy chain variable regions. Percentages in Tables 8 and 9 represent rounded values and in some cases may not equal 100% when added together. [000298] Amino acid length of the CDR3 region of IgM-primed VH1-69-derived heavy chains is shown in FIG. 21. Amino acid length of the CDR3 region of IgG-primed VH1-69-derived heavy chains is shown in FIG. 22. 61 iUUUL IMU. 10f UM-VVW [000299] As shown in Tables 8 and 9, mice according to the invention generate antigen specific antibodies containing VHi-69-derived heavy chains, which demonstrate a variety of rearrangements of a human VH1 -69 gene segment with a variety of human DH segments and human JH segments. Further, the antigen-specific antibodies contain cognate human light chains containing human VK domains resulting from a variety of rearrangements of human VK and JK gene segments. Table 6 Primer Sequence (5'-3') 3' Cg1 outer GGAAGGTGTG CACACCGCTG GAC (SEQ ID NO: 71) 3' Cg2ac outer GGAAGGTGTG CACACCACTG GAC (SEQ ID NO: 72) 3' Cg2b outer GGAAGGTGTG CACACTGCTG GAC (SEQ ID NO: 73) 3' Cg3 outer AGACTGTGCG CACACCGCTG GAC (SEQ ID NO: 74) 3' mIgM CH1 outer TCTTATCAGA CAGGGGGCTC TC (SEQ ID NO: 75) 3' mlgKC outer AAGAAGCACA CGACTGAGGC AC (SEQ ID NO: 76) Table 7 Primer Sequence (5'-3') 3' migGl/2b CHI inner AGTGGATAGA CWGATGGGGG TG (SEQ ID NO: 77) 3' mlgG2a/2c CH1 inner AGTGGATAGA CCGATGGGGC TG (SEQ ID NO: 78) 3' mIgG3 CH1 inner AAGGGATAGA CAGATGGGGC TG (SEQ ID NO: 79) 3' mIgM CH1 inner GGAAGACATT TGGGAAGGAC TG (SEQ ID NO: 80) 3' migKC-2 inner GGAAGATGGA TACAGTTGGT GC (SEQ ID NO: 81) 62 IJUUrKUL IMU. 14I Vf U%-VVUJ Table 8 Human DH 1gM IgG Human JH 1gM IgG 1-1 1.2 6.0 1 7.5 1.5 1-7 39.9 9.0 2 3.3 4.2 1-14 0.5 2.3 3 22.2 12.8 1-20 2.3 1.4 4 51.5 36.4 1-26 3.5 5.7 5 10.5 9.5 2-2 1.1 3.2 6 4.9 29.4 2-8 0.7 0.6 2-15 0.3 1.2 2-21 0.7 0.3 3-3 6.3 5.2 3-9 0.6 0.6 3-10 0.9 10.3 3-16 0.9 2.0 3-22 5.1 2.7 4-4/4-11 1.5 4.0 4-17 1.5 4.7 4-23 11.5 2.4 5-12 1.1 1.8 5-5/5-18 1.3 3.2 5-24 0.3 3.3 6-6 1.8 4.5 6-13 6.1 7.4 6-19 3.0 5.1 6-25 0.1 0.6 7-27 3.3 7.3 63 Table 9 Human VK % Observed Human JK % Observed 1-5 3.4 1 28.1 1-6 1.3 2 25.3 1-8 0 3 12.1 1-9 1.3 4 22.5 1-12 1.0 5 11.1 1-13 0 1-16 2.5 1-17 3.6 1-22 0 1-27 0.5 1-32 0 1-33 14.3 1-35 0 1-37 0 1-39 1.6 2-4 0 2-10 0 2-14 0 2-18 0 2-19 0 2-23 0 2-24 0.7 2-26 0 2-28 0 2-29 0 2-30 1.9 2-36 0 2-38 0 2-40 1.5 3-7 0 3-11 2.7 3-15 3.9 3-20 41.2 3-25 0 3-31 0 3-34 0 4-1 13.2 5-2 0.1 6-21 0 7-3 0 64

Claims

1. A mouse having a restricted immunoglobulin heavy chain locus characterized by the presence of a single human VH gene segment, one or more human DH gene segments, and one or more human JH gene segments, wherein the single human VH gene segment is a polymorphic VH gene segment.

2. The mouse of claim 1, wherein the mouse comprises a deletion of all or substantially all endogenous VH, DH, and JH gene segments.

3. The mouse of claim 1, wherein the single human VH gene segment is selected from VH1- 2 , VH1-69, VH2-26, VH 2 - 7 0, and VH 3 - 2 3 .

4. The mouse of claim 3, wherein the single human VH gene segment is VH1-69

5. The mouse of claim 3, wherein the single human VH gene segment is VHl-2.

6. The mouse of claim 1, wherein the single human VH gene segment is operably linked to a human or non-human immunoglobulin constant region gene.

7. The mouse of claim 6, wherein the immunoglobulin constant region gene is a mouse, rat, or human constant region gene.

8. The mouse of claim 1, further comprising a one or more human immunoglobulin VL gene segments operably linked to one or more human JL gene segments.

9. The mouse of claim 8, wherein the one or more human VL gene segments and/or the one or more human JL gene segments are selected from human K and human k gene segments.

10. The mouse of claim 8, wherein the one or more human immunoglobulin VL gene segments and one or more human JL gene segments are operably linked to a non-human light chain constant gene. 65 LJUFk""L EMU. I 0-I Uf6%"VV%.J

11. The mouse of claim 10, wherein the non-human light chain constant gene is selected from a mouse or rat K or X constant region gene.

12. A mouse comprising in its germline a replacement at an endogenous immunoglobulin heavy chain locus of all or substantially all endogenous VH, DH, and JH gene segments with single human VH gene segment and/or polymorphic variants thereof, one or more human DH gene segments and one or more human JH gene segments.

13. The mouse of claim 12, further comprising a replacement at an endogenous immunoglobulin light chain locus of all or substantially all endogenous VL and JL gene segments with one or more human VL and one or more human JL gene segments.

14. The mouse of claim 12, wherein the single human VH gene segment is selected from a human VH1-69 and a human VH1-2 gene segment.

15. A cell or tissue derived from the mouse of claim 1 or 12.

16. A method of making a nucleic acid sequence encoding a human VH domain comprising (a) immunizing a mouse of claim 1 or 12 with an antigen of interest; (b) allowing said mouse to mount an immune response to the antigen of interest; and, (c) obtaining a nucleic acid sequence encoding a human VH domain from said mouse.

17. The method of claim 16, wherein the immunoglobulin VH region sequence is at least 75% identical to SEQ ID NO: 34, SEQ ID NO: 36, SEQ ID NO: 38, SEQ ID NO: 40, SEQ ID NO: 42, SEQ ID NO: 44, SEQ ID NO: 46, SEQ ID NO: 48, SEQ ID NO: 50, SEQ ID NO: 52, SEQ ID NO: 54, SEQ ID NO: 56 or SEQ ID NO: 58.

18. The method of claim 16, wherein the immunoglobulin VH region sequence comprises SEQ ID NO: 34, SEQ ID NO: 36, SEQ ID NO: 38, SEQ ID NO: 40, SEQ ID NO: 42, SEQ ID NO: 44, SEQ ID NO: 46, SEQ ID NO: 48, SEQ ID NO: 50, SEQ ID NO: 52, SEQ ID NO: 54, SEQ ID NO: 56, SEQ ID NO: 58, or a polymorphic variant thereof.

19. The method of claim 16, wherein the immunoglobulin VH region sequence encodes a protein that is at least 75% identical with SEQ ID NO: 35, SEQ ID NO: 37, SEQ ID NO: 39, SEQ ID NO: 41, SEQ ID NO: 43, SEQ ID NO: 45, SEQ ID NO: 47, SEQ ID NO: 49, SEQ ID NO: 51, SEQ ID NO: 53, SEQ ID NO: 55, SEQ ID NO: 57 or SEQ ID NO: 59. 66 LUOUiKiN. I3IUM-VVV

20. The method of claim 16, wherein the immunoglobulin VH region sequence is at least 95% identical to SEQ ID NO: 60, SEQ ID NO: 62, SEQ ID NO: 64, SEQ ID NO: 66 or SEQ ID NO: 68.

21. The method of claim 16, wherein the immunoglobulin VH region sequence comprises SEQ ID NO: 60, SEQ ID NO: 62, SEQ ID NO: 64, SEQ ID NO: 66, SEQ ID NO: 68. or a polymorphic variant thereof.

22. The method of claim 16, wherein the immunoglobulin VH region sequence encodes a protein that is at least 95% identical with SEQ ID NO: 61, SEQ ID NO: 63, SEQ ID NO: 65, SEQ ID NO: 67 or SEQ ID NO: 69.

23. Use of a mouse according to claims 1 or 12 to make a nucleic acid sequence encoding a human heavy chain variable domain.

24. Use according to claim 23, wherein the human heavy chain variable domain is characterized by having human FR1-CDR1-FR2-CDR2-FR3 sequences derived from a polymorphic human VH gene segment.

25. Use according to claim 24, wherein the human VH gene segment is selected from a human VH1-2, VH1- 6 9 , VH2-26, VH 2 - 7 0, or VH3-23 gene segment.

26. Use according to claim 25, wherein the human VH gene segment is VH1-2.

27. Use according to claim 25, wherein the human VH gene segment is VH1 -69.

28. Use of a mouse according to claim 1 or 12 to make a human antibody, wherein the human antibody comprises a heavy chain variable domain derived from a rearranged human VH1-2 gene segment, human VH1-69 gene segment, or polymorphic variant thereof.

29. Use according to claim 28, wherein the rearranged human VH1-69 gene segment is at least 75% identical to SEQ ID NO: 34, SEQ ID NO: 36, SEQ ID NO: 38, SEQ ID NO: 40, SEQ ID NO: 42, SEQ ID NO: 44, SEQ ID NO: 46, SEQ ID NO: 48, SEQ ID NO: 50, SEQ ID NO: 52, SEQ ID NO: 54, SEQ ID NO: 56 or SEQ ID NO: 58. 67 LJU%,UAL IMU. I .I UVVJ

30. Use according to claim 28, wherein the rearranged human VH1-2 gene segment is at least 95% identical to SEQ ID NO: 60, SEQ ID NO: 62, SEQ ID NO: 64, SEQ ID NO: 66 or SEQ ID NO: 68. 68